15166 Federal Register / Vol. 87, No. 52 / Thursday, March 17, 2022 / Proposed Rules 

1EPA’s June 22, 2010 final action revoked the two 

1971 primary 24-hour standard of 140 ppb and the 

annual standard of 30 ppb because they were 

determined not to add additional public health 

protection given a 1-hour standard at 75 ppb. See 

75 FR 35520. However, the secondary 3-hour SO2

standard was retained. The 24-hour and annual 

standards became revoked for certain of those areas 

1 year after the effective date of when the EPA 

designated them for the 2010 1-hour SO2 NAAQS. 

See 40 CFR 50.4(e). 

FR 67249, November 9, 2000), because 

the SIP is not approved to apply in 

Indian country located in the state, and 

EPA notes that it will not impose 

substantial direct costs on tribal 

governments or preempt tribal law. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Nitrogen dioxide, Ozone, 

Reporting and recordkeeping 

requirements, Volatile organic 

compounds. 

Dated: March 8, 2022. 

Diana Esher, 

Acting Regional Administrator, Region III. 

[FR Doc. 2022–05403 Filed 3–16–22; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R03–OAR–2017–0615; FRL–9607–01– 

R3] 

Air Plan Partial Approval and Partial 

Disapproval; Pennsylvania; Attainment 

Plan for the Indiana, Pennsylvania 

Nonattainment Area for the 2010 Sulfur 

Dioxide Primary National Ambient Air 

Quality Standard 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to revise its 

prior action that fully approved a state 

implementation plan (SIP) revision 

submitted by the Commonwealth of 

Pennsylvania, through the Pennsylvania 

Department of Environmental Protection 

(PADEP), to EPA on October 11, 2017, 

and supplemented on February 5, 2020. 

The SIP revision provided a plan for 

attainment of the 2010 sulfur dioxide 

(SO2) primary national ambient air 

quality standard (NAAQS) in the 

Indiana, Pennsylvania SO2

nonattainment area (hereafter referred to 

as the ‘‘Indiana, PA NAA’’ or ‘‘Indiana 

Area’’). The attainment plan submission 

included a base year emissions 

inventory, an analysis of the reasonably 

available control technology (RACT) 

and reasonably available control 

measure (RACM) requirements, 

enforceable emission limitations and 

control measures, a reasonable further 

progress (RFP) plan, a modeling 

demonstration of SO2 attainment, and 

contingency measures for the Indiana 

Area. EPA is proposing to revise its 

prior action to partially approve and 

partially disapprove the SIP. This action 

is being taken under the Clean Air Act 

(CAA). 

DATES: Written comments must be 

received on or before April 18, 2022. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R03– 

OAR–2017–0615 at https://

www.regulations.gov, or via email to 

gordon.mike@epa.gov. For comments 

submitted at Regulations.gov, follow the 

online instructions for submitting 

comments. Once submitted, comments 

cannot be edited or removed from 

Regulations.gov. For either manner of 

submission, EPA may publish any 

comment received to its public docket. 

Do not submit electronically any 

information you consider to be 

confidential business information (CBI) 

or other information whose disclosure is 

restricted by statute. Multimedia 

submissions (audio, video, etc.) must be 

accompanied by a written comment. 

The written comment is considered the 

official comment and should include 

discussion of all points you wish to 

make. EPA will generally not consider 

comments or comment contents located 

outside of the primary submission (i.e. 

on the web, cloud, or other file sharing 

system). For additional submission 

methods, please contact the person 

identified in the FOR FURTHER

INFORMATION CONTACT section. For the 

full EPA public comment policy, 

information about CBI or multimedia 

submissions, and general guidance on 

making effective comments, please visit 

https://www.epa.gov/dockets/ 

commenting-epa-dockets. 

FOR FURTHER INFORMATION CONTACT: 

Megan Goold, Planning & 

Implementation Branch (3AD30), Air & 

Radiation Division, U.S. Environmental 

Protection Agency, Region III, 1650 

Arch Street, Philadelphia, Pennsylvania 

19103. The telephone number is (215) 

814–2027. Ms. Goold can also be 

reached via electronic mail at 

goold.megan@epa.gov. 

SUPPLEMENTARY INFORMATION: On 

October 11, 2017 and February 5, 2020, 

PADEP submitted a revision to its SIP 

for the purpose of providing for 

attainment of the 2010 SO2 primary 

NAAQS in the Indiana, PA NAA. 

I. Background 

On June 2, 2010, the EPA 

Administrator signed a final rule 

establishing a new primary SO2 NAAQS 

as a 1-hour standard of 75 parts per 

billion (ppb), based on a 3-year average 

of the annual 99th percentile of daily 

maximum 1-hour average 

concentrations. See 75 FR 35520 (June 

22, 2010), codified at 40 CFR 50.17. This 

action also provided for revoking the 

1971 primary, annual and 24-hour 

standards, subject to certain 

conditions.1 EPA established the 

NAAQS based on significant evidence 

and numerous health studies 

demonstrating that serious health effects 

are associated with short-term 

exposures to SO2 emissions ranging 

from five minutes to 24 hours, with an 

array of adverse respiratory effects 

including narrowing of the airways 

which can cause difficulty breathing 

(bronchoconstriction) and increased 

asthma symptoms. For more 

information regarding the health 

impacts of SO2, please refer to the June 

22, 2010, final rule. See 75 FR 35520. 

Following promulgation of a new or 

revised NAAQS, EPA is required by the 

CAA to designate areas throughout the 

United States as attaining or not 

attaining the NAAQS; this designation 

process is described in section 

107(d)(1)–(2) of the CAA. On August 5, 

2013, EPA promulgated initial air 

quality designations for 29 areas for the 

2010 SO2 NAAQS (78 FR 47191), which 

became effective on October 4, 2013, 

based on violating air quality 

monitoring data for calendar years 

2009–2011, where there was sufficient 

monitored data to support a 

nonattainment designation. 

Effective on October 4, 2013, the 

Indiana Area (which encompasses 

Indiana County, and Plumcreek 

Township, South Bend Township and 

Eldertown Borough of Armstrong 

County) was designated as 

nonattainment for the 2010 SO2 NAAQS 

for an area that encompasses the 

primary SO2 emitting sources: The 

Keystone, Conemaugh, Homer City, and 

Seward Electric Generating Units 

(EGUs). The October 4, 2013, final 

designation triggered a requirement for 

Pennsylvania to submit by April 4, 

2015, a SIP revision with an attainment 

plan for how the Indiana Area would 

attain the 2010 SO2 NAAQS as 

expeditiously as practicable, but no later 

than October 4, 2018, in accordance 

with CAA sections 110(a), 172(c) and 

191–192. 

For a number of areas, including the 

Indiana Area, EPA published a 

document on March 18, 2016, effective 

April 18, 2016, that Pennsylvania and 

other pertinent states had failed to 


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2Sierra Club, et al. v. EPA, Case No. 20–3568 (3rd 

Cir.). 

3See ‘‘Guidance for 1-Hour SO2 Nonattainment 

Area SIP Submissions’’ (April 23, 2014), available 

at https://www.epa.gov/sites/production/files/2016- 

06/documents/20140423guidance_nonattainment_

sip.pdf. 

submit the required SO2 attainment plan 

by this submittal deadline. See 81 FR 

14736. This finding initiated a deadline 

under CAA section 179(a) for the 

potential imposition of new source 

review and highway funding sanctions. 

However, pursuant to Pennsylvania’s 

submittal of October 11, 2017, and 

EPA’s subsequent completeness letter to 

Pennsylvania dated October 13, 2017, 

finding the submittal complete and 

noting the stopping of the sanctions’ 

deadline, these sanctions under section 

179(a) will not be imposed. 

Additionally, under CAA section 110(c), 

the March 18, 2016, finding triggered a 

requirement that EPA promulgate a 

Federal implementation plan (FIP) 

within two years of the effective date of 

the finding unless, by that time, the 

state has made the necessary complete 

submittal and EPA has approved the 

submittal as meeting applicable 

requirements. EPA took final action 

approving this attainment plan on 

October 19, 2020 (85 FR 66240), which 

removed the FIP obligation. 

On December 18, 2020, the Sierra 

Club, Clean Air Council, and 

PennFuture filed a petition for judicial 

review with the U.S. Court of Appeals 

for the Third Circuit, challenging that 

final approval.2 On April 5, 2021, EPA 

filed a motion for voluntary remand 

without vacatur of its approval of the 

Indiana, PA SO2 attainment plan. In its 

motion, EPA explained that as part of its 

plan Pennsylvania relied on a particular 

type of computer modeling (i.e., 

mathematical programs that project the 

impact of certain emissions limits on air 

quality). EPA had not previously 

approved use of this type of modeling 

in the context of SO2 attainment for the 

purpose of demonstrating that certain 

source emission limits with averaging 

times greater than one hour included in 

the plan would demonstrate attainment 

with the 2010 SO2 NAAQS. EPA further 

explained that a remand will allow EPA 

to revisit whether the specific modeling 

that Pennsylvania used to demonstrate 

that longer-term emission limits showed 

attainment was appropriate and will 

also allow EPA to further assess whether 

additional analyses are necessary to find 

that Pennsylvania has complied with 

the requirements of the CAA. Lastly, 

EPA explained that a remand will allow 

EPA to seek public comment on any 

new analyses and take other actions as 

appropriate. 

In a short order without any 

commentary, on August 17, 2021, the 

U.S. Court of Appeals for the Third 

Circuit granted EPA’s request for 

remand without vacatur of the final 

approval of Pennsylvania’s SO2

attainment plan for the Indiana, PA 

NAA, and required that EPA take final 

action in response to the remand no 

later than one year from the date of the 

court’s order (i.e., by August 17, 2022). 

This action proposes EPA’s response to 

the court’s order. 

After reconsideration, for reasons 

described in the following sections, EPA 

is proposing that it was incorrect to 

fully approve the Indiana, PA SO2

attainment plan, and is proposing to 

revise its action to disapprove portions 

of the Indiana, PA SO2 attainment plan 

while leaving certain other portions 

approved and while retaining 

incorporated emissions limits and 

control measures in the plan for limited 

SIP strengthening purposes. If EPA 

finalizes the partial disapproval 

proposed here, that action would 

initiate a sanctions clock under section 

179, providing for emission offset 

sanctions for new sources if EPA has not 

fully approved a revised plan within 18 

months after final partial disapproval, 

and providing for highway funding 

sanctions if EPA has not fully approved 

a revised plan within 6 months 

thereafter. The sanctions clock can be 

stopped only if the conditions of EPA’s 

regulations at 40 CFR 52.31 are met. A 

final partial disapproval would also 

initiate an obligation for EPA to 

promulgate a FIP within 24 months 

unless Pennsylvania has submitted, and 

EPA has fully approved, a plan 

addressing these attainment planning 

requirements. 

Attainment plans for SO2 must meet 

the applicable requirements of the CAA, 

and specifically CAA sections 110, 172, 

191, and 192. The required components 

of an SO2 attainment plan submittal are 

listed in section 172(c) of Title 1, part 

D of the CAA. EPA’s regulations 

governing SO2 nonattainment SIPs are 

set forth at 40 CFR part 51, with specific 

procedural requirements and control 

strategy requirements residing at 

subparts F and G, respectively. Soon 

after Congress enacted the 1990 

Amendments to the CAA, EPA issued 

comprehensive guidance on SIPs, in a 

document entitled the ‘‘General 

Preamble for the Implementation of 

Title I of the Clean Air Act Amendments 

of 1990,’’ published at 57 FR 13498 

(April 16, 1992) (General Preamble). 

Among other things, the General 

Preamble addressed SO2 SIPs and 

fundamental principles for SIP control 

strategies. Id. at 13545–49, 13567–68. 

On April 23, 2014, EPA issued 

guidance (hereafter ‘‘2014 SO2

Nonattainment Guidance’’) for how state 

submissions could address the statutory 

requirements for SO2 attainment plans.3

In this guidance, EPA described the 

statutory requirements for an attainment 

plan, which include: (1) An accurate 

base year emissions inventory of current 

emissions for all sources of SO2 within 

the nonattainment area (172(c)(3)); (2) 

an attainment demonstration that 

includes a modeling analysis showing 

that the enforceable emissions 

limitations and other control measures 

taken by the state will provide for 

expeditious attainment of the NAAQS 

(172(c) and (c)(6)); (3) demonstration of 

RFP (172(c)(2)); (4) implementation of 

RACM, including RACT (172(c)(1)); new 

source review (NSR) requirements 

(172(c)(5)); and (5) adequate 

contingency measures for the affected 

area (172(c)(9)). A synopsis of these 

requirements is provided in the notice 

of proposed rulemaking on the Illinois 

SO2 nonattainment plans, published on 

October 5, 2017, at 82 FR 46434. 

In order for the EPA to fully approve 

a SIP as meeting the requirements of 

CAA sections 110, 172 and 191–192 and 

EPA’s regulations at 40 CFR part 51, the 

SIP for the affected area must 

demonstrate to EPA’s satisfaction that 

each of the aforementioned 

requirements have been met. Under 

CAA sections 110(l) and 193, EPA may 

not approve a SIP that would interfere 

with any applicable requirement 

concerning NAAQS attainment and 

RFP, or any other applicable 

requirement, and no requirement in 

effect (or required to be adopted by an 

order, settlement, agreement, or plan in 

effect before November 15, 1990) in any 

area which is a nonattainment area for 

any air pollutant, may be modified in 

any manner unless it ensures equivalent 

or greater emission reductions of such 

air pollutant. 

CAA section 172(c)(1) directs states 

with areas designated as nonattainment 

to demonstrate that the submitted plan 

provides for attainment of the NAAQS. 

The provisions in 40 CFR part 51, 

subpart G, further delineate the control 

strategy requirements that SIPs must 

meet, and EPA has long required that all 

SIPs and control strategies reflect four 

fundamental principles of 

quantification, enforceability, 

replicability, and accountability (57 FR 

13567–68). SO2 attainment plans must 

consist of two components: (1) Emission 

limits and other control measures that 

assure implementation of permanent, 

enforceable, and necessary emission 

controls, and (2) a modeling analysis 


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4An ‘‘average year’’ is used to mean a year with 

average air quality. While 40 CFR part 50, appendix 

T, provides for averaging three years of 99th 

percentile daily maximum hourly values (e.g., the 

fourth highest maximum daily hourly concentration 

in a year with 365 days with valid data), this 

discussion and an example below uses a single 

‘‘average year’’ in order to simplify the illustration 

of relevant principles. 

meeting the requirements of 40 CFR part 

51, appendix W, which demonstrates 

that these emission limits and control 

measures provide for timely attainment 

of the primary SO2 NAAQS as 

expeditiously as practicable, but by no 

later than the attainment date for the 

affected area. In all cases, the emission 

limits and control measures must be 

accompanied by appropriate methods 

and conditions to determine compliance 

with the respective emission limits and 

control measures and must be 

quantifiable (a specific amount of 

emission reduction can be ascribed to 

the measures), fully enforceable 

(specifying clear, unambiguous and 

measurable requirements for which 

compliance can be practicably 

determined), replicable (the procedures 

for determining compliance are 

sufficiently specific and non-subjective 

so that two independent entities 

applying the procedures would obtain 

the same result), and accountable 

(source specific limits must be 

permanent and must reflect the 

assumptions used in the SIP 

demonstrations). 

EPA’s 2014 SO2 Nonattainment 

Guidance recommends that the 

emission limits established for the 

attainment demonstration be expressed 

as short-term average limits (e.g., 

addressing emissions averaged over one 

or three hours), but also describes the 

option to utilize emission limits with 

longer averaging times of up to 30 days 

so long as the state meets various 

suggested criteria. See 2014 SO2

Nonattainment Guidance, pp. 22 to 39. 

The guidance recommends that—should 

states and sources utilize longer 

averaging times—the longer-term 

average limit should be set at an 

adjusted level that reflects a stringency 

comparable to the 1-hour average limit 

at the critical emission value (CEV) 

shown to provide for attainment that the 

plan otherwise would have set. 

The 2014 SO2 Nonattainment 

Guidance provides an extensive 

discussion of EPA’s rationale for 

concluding that appropriately set, 

comparably stringent limitations based 

on averaging times as long as 30 days 

can be found to provide for attainment 

of the 2010 SO2 NAAQS. In evaluating 

this option, EPA considered the nature 

of the standard, conducted detailed 

analyses of the impact of 30-day average 

limits on the prospects for attaining the 

standard, and carefully reviewed how 

best to achieve an appropriate balance 

among the various factors that warrant 

consideration in judging whether a 

state’s plan provides for attainment. Id. 

at pp. 22–39, and Appendices B, C, and 

D. 

As specified in 40 CFR 50.17(b), the 

1-hour primary SO2 NAAQS is met at an 

ambient air quality monitoring site 

when the 3-year average of the annual 

99th percentile of daily maximum 1- 

hour average concentrations is less than 

or equal to 75 ppb. In a year with 365 

days of valid monitoring data, the 99th 

percentile would be the fourth highest 

daily maximum 1-hour value. The 2010 

SO2 NAAQS, including this form of 

determining compliance with the 

standard, was upheld by the U.S. Court 

of Appeals for the District of Columbia 

Circuit in Nat’l Envt’l Dev. Ass’n’s Clean 

Air Project v. EPA, 686 F.3d 803 (D.C. 

Cir. 2012). Because the standard has this 

form, a single exceedance does not 

create a violation of the standard. 

Instead, at issue is whether a source 

operating in compliance with a properly 

set longer term average could cause 

exceedances, and if so, the resulting 

frequency and magnitude of such 

exceedances, and in particular, whether 

EPA can have reasonable confidence 

that a properly set longer term average 

limit will provide that the average 

fourth highest daily maximum value 

will be at or below 75 ppb. A synopsis 

of how EPA evaluates whether such 

plans ‘‘provide for attainment,’’ based 

on modeling of projected allowable 

emissions and in light of the NAAQS’ 

form for determining attainment at 

monitoring sites, follows. 

For SO2 attainment plans based on 1- 

hour emission limits, the standard 

approach is to conduct modeling using 

fixed 1-hour emission rates. The 

maximum modeled emission rate that 

results in attainment is labeled the 

‘‘CEV.’’ The modeling process for 

identifying this CEV inherently 

considers the numerous variables that 

affect ambient concentrations of SO2, 

such as meteorological data, background 

concentrations, and topography. In the 

standard approach, the state would then 

provide for attainment by setting a 

continuously applicable 1-hour 

emission limit for each stationary SO2

source at this CEV. 

EPA recognizes that some sources 

have highly variable emissions, for 

example due to variations in fuel sulfur 

content and operating rate, that can 

make it extremely difficult, even with a 

well-designed control strategy, to ensure 

in practice that emissions for any given 

hour do not exceed the CEV. EPA also 

acknowledges the concern that longerterm emission limits can allow short 

periods with emissions above the CEV, 

which, if coincident with 

meteorological conditions conducive to 

high SO2 concentrations, could in turn 

create the possibility of a NAAQS 

exceedance occurring on a day when an 

exceedance would not have occurred if 

emissions were continuously controlled 

at the level corresponding to the CEV. 

However, for several reasons, EPA 

believes that the approach 

recommended in its guidance document 

suitably addresses this concern. First, 

from a practical perspective, EPA 

expects the actual emission profile of a 

source subject to an appropriately set 

longer-term average limit to be similar 

to the emission profile of a source 

subject to an analogous 1-hour average 

limit. EPA expects this similarity 

because it has recommended that the 

longer-term average limit be set at a 

level that is comparably stringent to the 

otherwise applicable 1-hour limit 

(reflecting a downward adjustment from 

the CEV) and that takes the source’s 

emissions profile (and inherent level of 

emissions variability) into account. As a 

result, EPA expects either form of 

emission limit to yield comparable air 

quality. 

Second, from a more theoretical 

perspective, EPA has compared the 

likely air quality with a source having 

maximum allowable emissions under an 

appropriately set longer term limit, as 

compared to the likely air quality with 

the source having maximum allowable 

emissions under the comparable 1-hour 

limit. In this comparison, in the 1-hour 

average limit scenario, the source is 

presumed at all times to emit at the 

CEV, and in the longer-term average 

limit scenario, the source is presumed 

occasionally to emit more than the CEV, 

but on average, and presumably at most 

times, to emit well below the CEV. In an 

‘‘average year,’’ 4 compliance with the 1- 

hour limit is expected to result in three 

exceedance days (i.e., three days with 

hourly values above 75 ppb) and a 

fourth day with a maximum hourly 

value at 75 ppb. By comparison, with 

the source complying with a longer-term 

limit, it is possible that additional 

exceedances would occur that would 

not occur in the 1-hour limit scenario (if 

emissions exceed the CEV at times 

when meteorology is conducive to poor 

air quality). However, this comparison 

must also factor in the likelihood that 

exceedances that would be expected in 

the 1-hour limit scenario would not 

occur in the longer-term limit scenario. 

This result arises because the longerterm limit requires lower emissions 


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5For example, if the CEV is 1000 pounds of SO2

per hour, and a suitable adjustment factor is 

determined to be 70 percent, the recommended 

longer term average limit would be 700 pounds per 

hour. 

6EPA published revisions to the ‘‘Guideline on 

Air Quality Models’’ on January 17, 2017. 

most of the time (because the limit is set 

below the CEV), so a source complying 

with an appropriately set longer-term 

limit is likely to have lower emissions 

at critical times than would be the case 

if the source were emitting as allowed 

with a 1-hour limit. 

To illustrate this point, EPA 

conducted a statistical analysis using a 

range of scenarios using actual plant 

data. The analysis is described in 

Appendix B of EPA’s 2014 SO2

Nonattainment Guidance. Based on the 

analysis described in the 2014 SO2

Nonattainment Guidance, EPA expects 

that an emission profile with maximum 

allowable emissions under an 

appropriately set, comparably stringent 

30-day average limit is likely to have the 

net effect of having a lower number of 

exceedances and better air quality than 

an emission profile with maximum 

allowable emissions under a 1-hour 

emission limit at the CEV. This result 

provides a compelling policy rationale 

for allowing the use of a longer 

averaging period, in appropriate 

circumstances where the facts indicate 

this result can be expected to occur. 

The 2014 SO2 Nonattainment 

Guidance offers specific 

recommendations for determining an 

appropriate longer-term average limit. 

The recommended method starts with 

determination of the 1-hour emission 

limit that would provide for attainment 

(i.e., the CEV), and applies an 

adjustment factor to determine the 

(lower) level of the longer-term average 

emission limit that would be estimated 

to have a stringency comparable to the 

otherwise necessary 1-hour emission 

limit. This method uses a database of 

continuous emission data reflecting the 

type of control that the source will be 

using to comply with the SIP emission 

limits, which (if compliance requires 

new controls) may require use of an 

emission database from another source. 

The recommended method involves 

using these data to compute a complete 

set of emission averages, computed 

according to the averaging time and 

averaging procedures of the prospective 

emission limitation (i.e., using 1-hour 

historical emission values from the 

emissions database to calculate 30-day 

average emission values). In this 

recommended method, the ratio of the 

99th percentile among these long-term 

averages to the 99th percentile of the 1- 

hour values represents an adjustment 

factor that may be multiplied by the 

candidate 1-hour emission limit (CEV) 

to determine a longer term average 

emission limit that may be considered 

comparably stringent.5

The 2014 SO2 Nonattainment 

Guidance also addresses a variety of 

related topics, including the potential 

utility of setting supplemental emission 

limits, such as mass-based limits, to 

reduce the likelihood and/or magnitude 

of elevated emission levels that might 

occur under the longer-term emission 

rate limit. 

Preferred air quality models for use in 

regulatory applications are described in 

Appendix A of the EPA’s ‘‘Guideline on 

Air Quality Models (40 CFR part 51, 

appendix W).’’ 6 In 2005, the EPA 

promulgated the American 

Meteorological Society/Environmental 

Protection Agency Regulatory Model 

(AERMOD) as the Agency’s preferred 

near-field dispersion modeling for a 

wide range of regulatory applications 

addressing stationary sources (for 

example, in estimating SO2

concentrations) in all types of terrain 

based on extensive developmental and 

performance evaluation. Supplemental 

guidance on modeling for purposes of 

demonstrating attainment of the SO2

standard is provided in Appendix A to 

the 2014 SO2 Nonattainment Guidance. 

Appendix A provides extensive 

guidance on the modeling domain, the 

source inputs, assorted types of 

meteorological data, and background 

concentrations. Consistency with the 

recommendations in this guidance is 

generally necessary for the attainment 

demonstration to offer adequately 

reliable assurance that the plan provides 

for attainment. 

As stated previously, attainment 

demonstrations for the 2010 1-hour 

primary SO2 NAAQS must demonstrate 

future attainment and maintenance of 

the NAAQS in the entire area 

designated as nonattainment (i.e., not 

just at the violating monitor) by using 

air quality dispersion modeling (see 

appendix W to 40 CFR part 51) to show 

that the mix of sources and enforceable 

control measures and emission rates in 

an identified area will not lead to a 

violation of the SO2 NAAQS. For a 

short-term (i.e., 1-hour) standard, EPA 

believes that dispersion modeling, using 

allowable emissions and addressing 

stationary sources in the affected area 

(and in some cases those sources located 

outside the nonattainment area which 

may affect attainment in the area) is 

technically appropriate, efficient and 

effective in demonstrating attainment in 

nonattainment areas because it takes 

into consideration combinations of 

meteorological and emission source 

operating conditions that may 

contribute to peak ground-level 

concentrations of SO2. 

The meteorological data used in the 

analysis should generally be processed 

with the most recent version of 

AERMET, the Meteorological data 

preprocessor for AERMOD. Estimated 

concentrations should include ambient 

background concentrations, should 

follow the form of the standard, and 

should be calculated as described in 

section 2.6.1.2 of the August 23, 2010 

clarification memo on ‘‘Applicability of 

Appendix W Modeling Guidance for the 

1-hr SO2 National Ambient Air Quality 

Standard’’ (U.S. EPA, 2010) and EPA’s 

March 11, 2011 clarification memo, 

‘‘Additional Clarification Regarding 

Application of Appendix W Modeling 

Guidance for the 1-hour NO2 National 

Ambient Air Quality Standard.’’ 

II. Summary of Pennsylvania’s SIP 

Revision and EPA Analysis 

In accordance with section 172(c) of 

the CAA, the Pennsylvania attainment 

plan for the Indiana Area includes: (1) 

An emissions inventory for SO2 for the 

plan’s base year (2011); and (2) an 

attainment demonstration. The 

attainment demonstration includes the 

following: (1) Analyses that locate, 

identify, and quantify sources of 

emissions contributing to violations of 

the 2010 SO2 NAAQS; (2) a 

determination that the control strategy 

for the primary SO2 sources within the 

nonattainment areas constitutes RACM/ 

RACT; (3) a dispersion modeling 

analysis of an emissions control strategy 

for the primary SO2 sources (Keystone, 

Conemaugh, Homer City, and Seward) 

purporting to show attainment of the 

SO2 NAAQS by the October 4, 2018, 

attainment date; (4) requirements for 

RFP toward attaining the SO2 NAAQS 

in the Area; (5) contingency measures; 

(6) the assertion that Pennsylvania’s 

existing SIP-approved NSR program 

meets the applicable requirements for 

SO2; and (7) the request that emission 

limitations and compliance parameters 

for Keystone, Conemaugh, Homer City, 

and Seward be incorporated into the 

SIP. 

On July 13, 2018 (83 FR 32606), EPA 

published a notice of proposed 

rulemaking (NPRM) in which EPA 

proposed full approval of 

Pennsylvania’s Indiana, PA SO2

attainment plan and SO2 emission limits 

and associated compliance parameters 

for the Keystone, Homer City, 

Conemaugh and Seward sources. During 


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7Sierra Club, et al. v. EPA, Case No. 20–3568 (3rd 

Cir.). 

8The AERR at subpart A to 40 CFR part 51 cover 

overarching federal reporting requirements for the 

states to submit emissions inventories for criteria 

pollutants to EPA’s Emissions Inventory System. 

EPA uses these submittals, along with other data 

sources, to build the National Emissions Inventory. 

9The CAA NSR program is composed of three 

separate programs: Prevention of significant 

deterioration (PSD), NNSR, and Minor NSR. PSD is 

established in part C of title I of the CAA and 

the public comment period, the Sierra 

Club (in conjunction with the National 

Parks Conservation Association, 

PennFuture, Earthjustice, and Clean Air 

Council) submitted a modeling analysis 

which showed that the emission limits 

in the attainment plan did not assure 

attainment because one modeled 

receptor within the nonattainment area 

had a modeled design value that was 

above the SO2 NAAQS. Sierra Club’s 

modeling also showed violations of the 

SO2 NAAQS outside of the 

nonattainment area. In response to this 

comment, on February 5, 2020, PADEP 

submitted supplemental information in 

support of the attainment plan. The 

February 5, 2020 submittal included: (1) 

A supplemental air dispersion modeling 

report; (2) supplemental air dispersion 

modeling data; (3) a supplemental air 

dispersion modeling protocol; (4) a 

meteorological monitoring plan; (5) 

meteorological monitoring data; (6) 

meteorological monitoring quality 

assurance, quality control, and audit 

reports; (7) Clean Air Markets Division 

(CAMD) emissions data for 2010–2018; 

and (8) Continuous Emissions 

Monitoring (CEM) data for 2010 through 

the third quarter of 2019. The 

supplemental air dispersion modeling 

used a more refined model receptor grid 

than that in the original submittal, 

meteorological data collected near the 

controlling modeled source (Seward), 

and more recent (2016–18) background 

concentrations from the South Fayette 

SO2 monitor (the monitor used to 

determine background concentrations in 

the original modeling analysis). The 

supplemental modeling did not address 

the violations occurring outside the 

nonattainment area that Sierra Club’s 

modeling identified. In order to allow 

for public comment on this 

supplemental information and 

modeling, on March 9, 2020 (85 FR 

13602), EPA published a notice of data 

availability (NODA) for the February 5, 

2020, submittal. During that public 

comment period, Sierra Club submitted 

new comments raising issues with the 

supplemental modeling. 

On October 19, 2020 (85 FR 66240), 

EPA finalized full approval of the 

Pennsylvania SO2 attainment plan for 

the Indiana, PA NAA (hereafter referred 

to as the ‘‘October 2020 final rule 

action’’ or the ‘‘October 2020 final 

action’’). On December 18, 2020, the 

Sierra Club, Clean Air Council, and 

PennFuture filed a petition for judicial 

review with the U.S. Court of Appeals 

for the Third Circuit, challenging that 

final approval.7 As mentioned earlier, 

on August 17, 2021, the U.S. Court of 

Appeals for the Third Circuit granted 

EPA’s request for remand without 

vacatur of the final approval of 

Pennsylvania’s SO2 attainment plan for 

the Indiana, PA NAA. The court ordered 

EPA to take final action to respond to 

the remand no later than August 17, 

2022. EPA has reconsidered that final 

action and is proposing to revise its 

prior full approval to a partial approval 

and partial disapproval based on the 

analysis and explanation below. EPA 

now proposes to determine that it was 

in error to fully approve the Indiana, PA 

SO2 attainment plan, and is in the same 

manner as the prior full approval 

revising its prior action. See, CAA 

section 110(k)(6). EPA is proposing to 

retain the approval of the emissions 

inventory and nonattainment New 

Source Review (NNSR) program 

requirements, and is proposing 

disapproval of the attainment 

demonstration, RACM/RACT 

requirements, RFP requirements and 

contingency measures. 

A. Emissions Inventory Requirements 

States are required under section 

172(c)(3) of the CAA to develop 

comprehensive, accurate and current 

emissions inventories of all sources of 

the relevant pollutant or pollutants in 

the nonattainment area. These 

inventories provide detailed accounting 

of all emissions and emissions sources 

of the pollutant or precursors. In 

addition, inventories are used in air 

quality modeling to demonstrate that 

attainment of the NAAQS is as 

expeditious as practicable. The SO2

Nonattainment Guidance provides that 

the emissions inventory should be 

consistent with the Air Emissions 

Reporting Requirements (AERR) at 

Subpart A to 40 CFR part 51.8

For the base year inventory of actual 

emissions, a ‘‘comprehensive, accurate 

and current’’ inventory can be 

represented by a year that contributed to 

the three-year design value used for the 

original nonattainment designation. The 

2014 SO2 Nonattainment Guidance 

notes that the base year inventory 

should include all sources of SO2 in the 

nonattainment area as well as any 

sources located outside the 

nonattainment area which may affect 

attainment in the area. Pennsylvania 

appropriately elected to use 2011 as the 

base year because the designation of 

nonattainment was based on data from 

2009–2011. Actual emissions from all 

the sources of SO2 in the Indiana Area 

were reviewed and compiled for the 

base year emissions inventory 

requirement. The primary SO2-emitting 

point sources located within the Indiana 

Area are Keystone, Conemaugh, Homer 

City, and Seward, all coal-fired power 

plants. Keystone and Conemaugh each 

have two pulverized coal-fired (PC) 

boilers; Homer City has three coal-fired 

boilers; and Seward has two circulating 

fluidized bed (CFB) waste coal-fired 

boilers. More information about the 

emissions inventory for the Indiana 

Area (and analysis of the inventory) can 

be found in Pennsylvania’s October 11, 

2017, submittal as well as EPA’s 

emissions inventory technical support 

document (TSD), which can be found 

under Docket ID No. EPA–R03–OAR– 

2017–0615 and online at 

www.regulations.gov. 

Table 1 in this document shows the 

level of emissions, expressed in tons per 

year (tpy), in the Indiana Area for the 

2011 base year by emissions source 

category. The point source category 

includes all sources within the Area. 

TABLE 1—2011 BASE YEAR SO2

EMISSIONS INVENTORY FOR THE INDIANA AREA

Emission source category SO2 emissions 

(tpy) 

Point ...................................... 144,269.017 

Area ...................................... 555.610 

Non-road ............................... 1.025 

On-road ................................. 7.730 

Total ............................... 144,833.382 

EPA has evaluated Pennsylvania’s 

2011 base year emissions inventory for 

the Indiana Area and has made the 

preliminary determination that this 

inventory was developed in a manner 

consistent with EPA’s guidance and that 

EPA appropriately approved this 

element of the attainment plan in its 

prior action. Therefore, pursuant to 

section 172(c)(3), EPA is not proposing 

to change its approval of Pennsylvania’s 

2011 base year emissions inventory for 

the Indiana Area to a disapproval, as it 

meets CAA requirements. Instead, EPA 

is proposing that the plan retain its 

approval with respect to the base year 

emissions inventory element. 

B. New Source Review 9

Section 172(c)(5) of the CAA requires 

that an attainment plan require permits 


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applies in undesignated areas and in areas that meet 

the NAAQS—designated ‘‘attainment areas’’—as 

well as areas where there is insufficient information 

to determine if the area meets the NAAQS— 

designated ‘‘unclassifiable areas.’’ The NNSR 

program is established in part D of title I of the CAA 

and applies in areas that are not in attainment of 

the NAAQS—designated ‘‘nonattainment areas.’’ 

The Minor NSR program addresses construction or 

modification activities that do not qualify as 

‘‘major’’ and applies regardless of the designation 

of the area in which a source is located. Together, 

these programs are referred to as the NSR programs. 

Section 173 of the CAA lays out the NNSR program 

for preconstruction review of new major sources or 

major modifications to existing sources, as required 

by CAA section 172(c)(5). The programmatic 

elements for NNSR include, among other things, 

compliance with the lowest achievable emissions 

rate and the requirement to obtain emissions offsets. 

10The period of meteorological data needed for 

an air-quality analysis is described in section 8.4.2 

(e) of appendix W: ‘‘[T]he use of five years of 

adequately representative National Weather Service 

or comparable meteorological data, at least one year 

of site-specific, or at least three years of prognostic 

meteorological data, are required.’’ 

11A detailed discussion of the deficiencies of the 

AERMOIST modeling analysis submitted for the 

Indiana Area can be found in EPA’s AERMOIST 

modeling TSD for the Indiana Area which can be 

found under Docket ID No. EPA–R03–OAR–2017– 

0615 and available online at www.regulations.gov. 

12Refer to EPA’s Modeling TSDs for the Indiana 

Area under Docket ID EPA–R03–OAR–2017–0615, 

available at www.regulations.gov for EPA’s review 

of the modeling domains (TSD For the Modeling 

Portions of the Document Entitled ‘‘State 

Implementation Plan Revision: Attainment 

Demonstration and Base Year Inventory Indiana, PA 

Continued 

for the construction and operation of 

new or modified major stationary 

sources in a nonattainment area. 

Pennsylvania has a fully implemented 

Nonattainment New Source Review 

(NNSR) program for criteria pollutants 

in 25 Pennsylvania Code Chapter 127, 

Subchapter E, which was approved into 

the Pennsylvania SIP on December 9, 

1997 (62 FR 64722). On May 14, 2012 

(77 FR 28261), EPA approved a SIP 

revision pertaining to the preconstruction permitting requirements of 

Pennsylvania’s NNSR program to 

update the regulations to meet EPA’s 

2002 NSR reform regulations. EPA then 

approved an update to Pennsylvania’s 

NNSR regulations on July 13, 2012 (77 

FR 41276), and on June 11, 2021 (86 FR 

25951). These rules provide for 

appropriate NSR as required by CAA 

sections 172(c)(5) and 173 and 40 CFR 

51.165 for SO2 sources undergoing 

construction or major modification in 

the Indiana Area without need for 

modification of the approved rules. 

Therefore, in its prior approval action, 

EPA concluded that the Pennsylvania 

SIP meets the requirements of section 

172(c)(5) for the Indiana Area. EPA 

continues to believe that the 

Pennsylvania SIP meets this 

requirement and is not proposing to 

change its action to disapproval for the 

NNSR element. Instead, EPA is 

proposing that the plan retain its 

approval with respect to the NNSR 

element. 

C. Attainment Demonstration 

The SO2 attainment demonstration 

provides air quality dispersion 

modeling analyses intended to 

demonstrate that control strategies 

chosen to reduce SO2 source emissions 

will bring the area into attainment by 

the statutory attainment date of October 

4, 2018. The modeling analyses are used 

to assess the control strategy for a 

nonattainment area and establish 

emission limits that will provide for 

attainment. The analyses require five 

years of meteorological data to simulate 

the dispersion of pollutant plumes from 

multiple point, area, or volume sources 

across the averaging times of interest.10

The modeling demonstration typically 

also relies on maximum allowable 

emissions from sources in the 

nonattainment area. Modeling analyses 

that provide for attainment under all 

scenarios of operation for each source 

must, therefore, consider the worst-case 

scenario of both the representative 

meteorology (e.g., predominant wind 

directions, stagnation, etc.) and the 

maximum allowable emissions. In this 

way, the attainment demonstration 

shows that the emissions limits in the 

SIP provide for attainment under all 

worst-case meteorological and 

emissions scenarios that are permissible 

under the limits. 

In its October 11, 2017, and February 

5, 2020, submissions, PADEP provided 

multiple modeling analyses as their 

attainment demonstration. In order to 

better explain our review of each 

analysis, EPA has categorized them— 

first to address Pennsylvania’s request 

to use an alternative model option 

(AERMOIST) in the attainment plan, 

and then to address the modeling used 

to develop emission limits for the four 

main sources of SO2 emissions. This is 

the same approach EPA used to review 

the modeling analyses for the October 

2020 final rule action that fully 

approved the plan. 

In relation to the alternative model 

request, PADEP provided: (1) An 

analysis using the default option in 

EPA’s preferred dispersion modeling 

system, AERMOD; and (2) an analysis 

utilizing AERMOD but including a 

procedure called AERMOIST, an 

alternative model option which 

accounts for additional plume rise 

associated with the latent heat release of 

condensation due to moisture in a 

stack’s plume. AERMOIST is currently 

not approved by EPA for regulatory use. 

On July 13, 2018, EPA rejected 

PADEP’s request to use AERMOIST in 

its attainment demonstration. 83 FR 

32606. EPA is not proposing to change 

our previous rejection of the AERMOIST 

procedure in this action, nor did we in 

the October 2020 final action. EPA’s 

conclusion from its review of 

AERMOIST in the previous action still 

applies, which was that the AERMOIST 

procedure is not an appropriate option 

for use in the Indiana attainment plan 

for the following reasons: (1) There is no 

multi-monitor database of SO2

monitoring data available for the four 

major sources of SO2 in the Indiana 

Area to conduct a source-specific 

statistical test to determine if 

AERMOIST provides a definitive 

improvement over the current 

regulatory default version of AERMOD; 

(2) AERMOIST was universally applied 

to all the major sources in the Indiana 

Area regardless of whether the source 

plumes are actually saturated; and (3) 

there is a lack of supporting analysis for 

using relative humidity measurements 

in AERMOIST.11

PADEP submitted multiple additional 

modeling analyses not relying upon 

AERMOIST to develop and/or support 

emission limits for the four main 

sources of SO2 emissions in the Indiana 

Area: (1) A February 5, 2020 modeling 

analysis using randomly reassigned 

emission (RRE) values to support the 30- 

day limit for Seward; (2) an October 11, 

2017 modeling analysis using RRE 

values to support the 30-day limit for 

Seward; (3) an October 11, 2017 

modeling analysis using RRE values to 

develop a 24-hour emission limit for 

Keystone; (4) a February 5, 2020 

modeling analysis to reexamine the 

Critical Emission Value (CEVs) for 

Keystone, Conemaugh, Homer City and 

Seward; and (5) an October 11, 2017 

modeling analysis to determine the 

CEVs for the four main SO2 sources: 

Keystone, Conemaugh, Homer City and 

Seward. 

In the October 2020 final action, EPA 

focused our review on the CEV and RRE 

modeling from the February 5, 2020, 

submittal used to support Seward’s 

longer-term limit and on review of the 

CEV and RRE modeling in the October 

11, 2017 submittal used to develop 

Keystone’s longer-term limit. Our 

reconsideration of these reviews, and 

the reasons for why we now think we 

were in error to fully approve the 

analyses, is explained in detail below. 

EPA reviewed the October 11, 2017, 

and the February 5, 2020, modeling 

analyses, which were used by PADEP to 

determine the CEVs for Keystone, 

Conemaugh, Seward and Homer City.12


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Nonattainment Area for the 2010 1-Hour Sulfur 

Dioxide National Ambient Air Quality Standard,’’ 

dated October 2017 pages 9–14, and TSD For the 

Modeling Portions of the Document Entitled 

‘‘Supplemental Information to Address a Comment 

Received by the EPA on Pennsylvania’s 1-hour 

Sulfur Dioxide Attainment Demonstration for the 

Indiana, Pennsylvania Nonattainment Area’’ 

submitted on February 5, 2020 pages 12–15) and 85 

FR 66240 at 66247–66248. 

13Plan Approval 32–00055H was issued on April 

2, 2012, and modified on April 4, 2013, by PADEP. 

14Based on the National Institute of Standards 

and Technology conversion: 1 pound = 453.59237 

grams 

15While the current CEV modeling is not a reason 

for disapproval, as discussed later in the preamble, 

EPA encourages Pennsylvania to ensure that the 

revised attainment plan includes modeling that 

provides for attainment in all areas with known 

NAAQS violations. 

In the October 11, 2017, submittal, the 

Indiana Area was divided into two 

separate modeling domains. One 

domain included portions of Armstrong 

County which only addressed emissions 

from Keystone as a source. The other 

domain covered all of Indiana County 

and addressed emissions from all four 

sources in the nonattainment area. For 

both domains, background 

concentrations included impacts from 

non-modeled sources. Each separate 

model domain used its own (different) 

background concentration. EPA 

continues to agree with Pennsylvania 

that two modeling domains are 

appropriate due to the long distance 

between Keystone and the other three 

sources, and the predominant wind 

direction. EPA also continues to assert 

that the use of a different, and higher 

background for the Keystone CEV 

modeling, while not required, provides 

additional assurances that the CEV for 

Keystone is protective of the NAAQS. 

85 FR 66420. 

AERMOD was used to determine the 

CEVs for Conemaugh, Keystone, and 

Seward where the modeled 1-hour 

emission rates demonstrate attainment 

of the 2010 1-hour SO2 NAAQS. The 

SO2 emission rates for Homer City were 

based on the unit 1, unit 2, and unit 3 

combined mass-based SO2 emission 

limits established in Plan Approval 32– 

00055H,13 which authorized the 

installation of Novel Integrated 

Desulfurization (NID) systems, often 

referred to as Dry Flue Gas 

Desulphurization (FGD) systems on unit 

1 and unit 2. This 1-hour SO2 limit was 

based on air dispersion modeling that 

demonstrated attainment of the 2010 1- 

hour SO2 NAAQS. 

In the February 5, 2020, modeling 

analysis, an alternative finer scale grid 

in the southeast corner of the original 

Indiana County domain was used, as 

well as multi-level site-specific 

meteorological data that were generated 

during the period from September 2015 

through August 2016, and updated 

background concentrations. When all 

the updates were modeled, Seward’s 1- 

hour CEV had to be reduced 

approximately 11% from the original 

CEV to show attainment with the 

NAAQS (CEV changed from 5,079 lb/hr 

to 4,500 lb/hr). The CEVs for the other 

three SIP sources did not change. The 

CEV rates used in the demonstration 

analysis for each of the four sources are 

summarized in the following table. The 

modeled emission rate in grams per 

second was converted to pounds per 

hour, which is the CEV for each 

source.14 Upon reconsideration, EPA is 

not proposing to change the October 

2020 decision that the CEVs were 

modeled correctly.15

TABLE 2—FEBRUARY 5, 2020 MODEL RUN RESULTS—CRITICAL EMISSION VALUES

Source 

Critical emission value - 

SO2 emission rates 

modeled in attainment 

model run (g/s) 

Critical emission value - 

SO2 emission rates 

modeled in attainment 

model run (lb/hr) 

Seward ..................................................................................................................................... 566.99 4500.0 

Homer City Unit 1 .................................................................................................................... 195.30 1550.0 

Homer City Unit 2 .................................................................................................................... 195.30 1550.0 

Homer City Unit 3 .................................................................................................................... 410.75 3260.0 

Keystone .................................................................................................................................. 1223.60 9711.1 

Conemaugh ............................................................................................................................. 426.00 3381.0 

The October 11, 2017, submittal also 

included a modeling analysis using 

randomly reassigned historical hourly 

emissions for Keystone for 100 

AERMOD simulations (referred to as 

RRE Modeling). The hourly modeled 

emission values were based on 2016 

actual hourly emissions that reflect 

emission patterns based on plant 

operations and reassigned to determined 

fixed values through a binning approach 

in which the upper limit for each 

corresponding bin was used as the 

modeled emission rate. The emissions 

profile was such that the actual 

emission rate for 15% of the hours per 

year were above the CEV of 9,711 lb/hr, 

and those hours fell within 15 days in 

each month. Because of this pattern, 

where hourly actual emissions values 

above the CEV were clustered together 

on a limited number of days rather than 

individually dispersed throughout the 

year, Pennsylvania created a ‘‘rule’’ in 

the modeling of binned reassigned fixed 

values, whereby the actual hours over 

the CEV were modeled in separate 

clusters which Pennsylvania calls ‘‘high 

emission event days.’’ The total amount 

of SO2 emissions each day, however, are 

constrained by a limit which restricts 

the total pounds of SO2 emissions, on a 

24-hour block average basis, to be at or 

below 9,600 lb/hr. The hours for which 

the emissions were modeled above the 

CEV were not randomly dispersed 

individually throughout the year 

because the plant did not and likely will 

not operate that way in order to meet 

the limit. Thus, these high emission 

events were modeled in a way that is 

representative of the variability in the 

historic (2016) emissions data and of 

expected emissions performance 

occurring in compliance with the 

allowable emissions limit (as asserted in 

Pennsylvania’s submittal). 

The ‘‘rule’’ constrained the high 

emission events days to not exceed 

9,604 lb/hr on a 24-hour block average; 

however, not every day was modeled 

with hourly emission rates resulting in 

a 24-hour block average approaching or 

equal to 9,604 lbs/hr. As previously 

described, the historical emissions data 

demonstrate that not every day is a high 

emission event day based on the historic 

variability of the source. Pennsylvania 

modeled about 50% of the days in a 

month where binned reassigned hourly 

SO2 emissions were always below the 

CEV value and about 50% of the days 

in a month as high emission event days 

where there were at least three hours of 

binned reassigned emissions over the 

CEV during those 24 hours. The high 


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16See EPA’s March 1, 2011 clarification memo 

‘‘Additional Clarification Regarding Application of 

Appendix W Modeling Guidance for the 1-hour 

NO2 National Ambient Air Quality Standard.’’ 

emission events days included nine 

days (30% of the days) in a month 

where the 24-hour averages were near 

9,600 lb/hr. The remaining six high 

emission event days per month 

experienced three hours of emissions 

above the CEV, yet emissions during the 

remaining hours of the day resulted in 

the 24-hour daily average falling at 

6,333 lb/hr for five of the six days and 

at 8,964 lb/hr for one of the six days. 

However, the other hours in these days 

were assigned values at or below the 

CEV, reflecting the predominance of 

values below the CEV in the modeled 

emissions distribution (which in turn 

reflected the predominance of values 

below the CEV in the historical record), 

resulting in daily average emission rates 

for these days below 9,600 lb/hr. The 

remaining days (not categorized as high 

emission events days) had 24-hour daily 

average emissions between 5,000 lb/hr 

and 6,200 lb/hr. 

Pennsylvania developed 100 different 

annual emission profiles using the 

historic data of high emission event 

days, and randomly re-assigning the 

other hourly emissions such that the 24- 

hour limit of 9,600 lbs/hr is modeled 

during 30% of the days across each 

month. These emission files provide a 

large array of temporally varying hourly 

actual emissions which take into 

account the ‘‘rule’’ where hourly actual 

emissions above the CEV are clustered 

together into high emission event days, 

reflecting the variability in the historic 

emissions data and historic plant 

operations. Each of the 100 emissions 

scenarios were modeled with five years 

of meteorological data using AERMOD. 

For each of the 100 5-year AERMOD 

simulations for Keystone, the 5-year 

average of the 99th percentile of the 

daily maximum 1-hour SO2 modeled 

concentrations were below the 

NAAQS.16

When reconsidering the RRE 

modeling for Keystone, EPA examined 

whether the RRE modeling provided the 

necessary analysis to determine if the 

longer term limits were comparably 

stringent to the modeled 1-hour CEVs 

and whether the RRE approach 

demonstrated that the longer term limits 

provided for attainment. 

While the 2014 SO2 Nonattainment 

Guidance did not preclude states from 

using other approaches to determine 

appropriate longer term average limits, 

EPA did recommend that in all cases the 

analysis begin with the determination of 

the CEV (a constant hourly emissions 

level at which attainment is modeled to 

occur) and include an assessment 

showing that the longer term limits are 

of comparable stringency to the 1-hour 

CEV. This is a critical element in the 

attainment demonstration because it 

provides a similar level of assurance 

that complying with the longer term 

limit, in lieu of the hourly limit 

reflecting the modeled CEV, will also 

provide for attainment. 

As described earlier, Pennsylvania 

provided adequate CEV modeling for 

Keystone, Seward, Homer City, and 

Conemaugh, but Pennsylvania did not 

provide evidence that the longer term 

limits derived via the application of 

RRE modeling were comparable in 

stringency to the 9,711 lb/hr CEV for 

Keystone. Essentially, the necessary 

steps to establish the comparably 

stringent relationship between a 

modeled 1-hour CEV and longer term 

limits were not taken. 

In the October 2020 final rule action, 

EPA did not address whether the longer 

term limits derived via the RRE 

modeling of binned reassigned 

historical emissions were in fact 

comparably stringent to the 1-hour CEV, 

and at that time only focused our review 

on whether the RRE modeling of binned 

re-assigned historical actual emissions 

projected future emissions performance 

that would result in NAAQS attainment. 

In that final rule, EPA stated that ‘‘the 

RRE modeling provided enough 

permutations of emissions and 

meteorology that we can be reasonably 

confident that Keystone’s longer-term 

limit is protective of the NAAQS. This 

conclusion is based upon the large 

number of emission distribution profiles 

(100), the frequency and distribution of 

high emission event days, the 9,600 lb/ 

hr 24-hour emission limit modeled 30% 

of the days per month, emissions inputs 

reflective of the variability in historic 

plant operations, and meteorological 

data (five years of National Weather 

Service data).’’ (85 FR 66240 at 66244). 

Upon reconsideration, EPA has 

determined that without a comparably 

stringent analysis and a clear link 

between the modeled 1-hour CEV and 

the longer term limit, EPA does not have 

adequate assurance that Keystone’s 

longer term limit, considering worst 

case emissions scenarios permissible 

under the limit, is protective of the 1- 

hour SO2 standard. EPA did not address 

this issue clearly in the October 2020 

final action; however, EPA was clear in 

the 2014 SO2 Guidance, which states, 

‘‘A comparison of the 1-hour limit and 

the proposed longer term limit, in 

particular an assessment of whether the 

longer term average limit may be 

considered to be of comparable 

stringency to a 1-hour limit at the 

critical emission value, would be a 

critical element of a demonstration that 

any longer term average limits in the SIP 

will help provide adequate assurance 

that the plan will provide for attainment 

and maintenance of the 1-hour 

NAAQS.’’ (pg. 26). 

In addition to not having established 

that the longer term limits are 

comparably stringent to the 1-hour CEV, 

Pennsylvania’s binning approach used 

in the RRE modeling was dependent 

upon historical emissions performance 

and assumed continued performance 

that was well below that which is 

permissible under the limit. The binned 

emissions approach may have been a 

valid way to characterize factual air 

quality resulting from actual emissions 

and may be useful in a designations or 

attainment determination context. 

However, because the approach did not 

characterize maximally possible 

emissions that could occur in 

compliance with the emission limit nor 

provide a comparably stringent analysis, 

EPA now considers that it falls short of 

demonstrating that the limits will 

provide for attainment under all worst 

case emissions scenarios that are 

permissible under the limit, and that it 

was incorrect for EPA to fully approve 

the attainment demonstration in the 

absence of this demonstration. 

In order to establish the comparable 

stringency of a longer term limit to a 

modeled attaining 1-hour CEV, EPA’s 

2014 Guidance recommended using a 

comparison of the 99th percentile of 

historic hourly emissions to the 99th 

percentile of the longer term averaged 

emissions of the same dataset to develop 

an adjustment factor for use in 

converting the modeled 1-hour CEV to 

a comparably stringent longer term 

limit. The focus on the 99th percentile 

of data is purposeful to ensure that 

extreme hourly variability was correctly 

accounted for in developing the longer 

term limits and showing that the longer 

term limits account for the worst case 

emissions performance that is 

permissible under the limits. Generally, 

when applying EPA’s recommended 

methodology for developing a 

comparably stringent longer term limit, 

a source with a history of frequent 

spikes of high hourly emissions will 

have a lower adjustment factor, 

resulting in a greater reduction in the 

numeric value of the comparably 

stringent longer term limit, than a 

source with less frequent spikes of high 

hourly emissions. Development of a 

longer term limit based on a variability 

metric other than the 99th percentile 

metric of the historic emissions 

variability should be accompanied by 


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17This CEV and the description provided are 

based on Pennsylvania’s updated analysis which 

was provided to EPA on February 5, 2020. The CEV 

for Seward in the October 11, 2018 submittal was 

5,079 lb/hr. 

justification of how the longer term 

limit is comparably stringent to the 1- 

hour CEV. In the RRE analysis for 

Keystone, the Commonwealth of 

Pennsylvania used the actual hourly 

emissions distribution of one year 

(2016) to generate 100 hourly emissions 

profiles to use in the modeling. 

Pennsylvania’s analysis (i.e., RRE 

approach) was an assessment of hourly 

emissions with no assurance (via a 

comparably stringent consideration) that 

prospective (future) hourly emissions 

when complying with the longer term 

limit (potentially worst case scenarios) 

were properly accounted for. 

Pennsylvania did not provide a 

justification for using a metric other 

than the 99th percentile of hourly 

emissions data to support Keystone’s 

longer-term limit. This means that 

Pennsylvania did not establish that the 

longer term limit for Keystone was 

comparably stringent to an attaining 1- 

hour CEV, and that EPA erred in 

approving the attainment demonstration 

and limit as providing for NAAQS 

attainment. Thus, EPA is proposing to 

correct its prior approval to a 

disapproval of the attainment 

demonstration for Keystone. 

In the February 5, 2020, submittal, 

Pennsylvania included an RRE analysis 

for Seward to support its already 

established 30-day average SO2 limit of 

3,038.4 lb/hr. First, Pennsylvania 

determined Seward’s CEV of 4,500 lb/hr 

using AERMOD.17 Then, using 2016– 

2018 emissions from Seward, 

Pennsylvania developed a binned 

emissions dataset to be used in 

formulating the inventories modeled in 

100 AERMOD simulations. 

Pennsylvania used a total of 13 bins, 

including five bins ranging from an 

upper level of 2,000 lbs/hour to an 

upper level of 4,500 lbs/hour and eight 

bins at various ranges above the CEV. 

Hours without operation were 

represented as hours with 2,000 lbs/ 

hour, and all the other hours were 

represented with the upper level of the 

applicable bin. The dataset included 

2.5% of hourly emissions above the CEV 

(or 220 hours). This was based on how 

the plant historically operated while 

complying with this 30-day limit during 

the appliable time period and how it is 

expected to operate into the future 

while in compliance with the 30-day 

limit. The hours above the CEV were 

distributed across four high emission 

events, where the duration of each event 

was 4, 7, 12, or 16 hours, with the 

frequency of those events being twice 

per month, monthly, every six months 

and once per year, respectively, such 

that these 220 hours above the CEV 

were spread across 39 days. The 

remaining 97.5% of hourly emissions 

were below the CEV and randomly 

assigned throughout the annual 

emissions profile. 

Pennsylvania calculated a weighted 

average of the hourly emissions in the 

binned inventory by multiplying the bin 

level times the percentage of hours in 

each bin and summing the results. This 

sum, representing the average of the 

modeled emissions, equaled 3,088 lb/hr. 

Despite minor variations resulting from 

the random distribution process, each of 

the 100 AERMOD simulations had 

approximately this average level of 

emissions. 

Pennsylvania developed 100 different 

annual emission profiles using the 

historic data of high emission event 

days, and randomly assigning the other 

hourly emissions such that the average 

of the 30-day averages of each 

simulation was close to 3,088 lb/hr. 

Seward’s SO2 emissions limit of 3,038.4 

lb/hr on a 30-day rolling average basis 

is approximately 50 lb/hr less than the 

approximate average emissions value 

used in the AERMOD simulations. 

As similarly described above for 

Keystone, when reconsidering the RRE 

modeling for Seward, EPA has now 

examined whether the RRE modeling 

provided the necessary analysis to 

determine if the longer term limits were 

comparably stringent to the modeled 1- 

hour CEVs. Upon reconsideration, EPA 

has found that the RRE modeling used 

to support Seward’s longer term limit 

did not provide evidence that the longer 

term limit is comparably stringent to 

Seward’s CEV of 4,500 lb/hr. As noted 

previously in the preamble, the CEV for 

Seward decreased 11% from 5,079 lb/hr 

in the October 11, 2017, submittal to 

4,500 lb/hr in the February 5, 2020, 

submittal, due to updates to model 

inputs, in particular, site specific 

meteorology data, a more refined 

receptor grid, and updated emissions 

data. The RRE derived longer-term limit, 

however, did not change from one 

submittal to the next. This highlights 

the failed linkage of the modeled CEV 

to this longer term limit. In the October 

2020 final action, EPA failed to address 

this critical element in determining 

whether the State had adequately shown 

that allowable emissions performance in 

compliance with a longer term limit for 

Seward ensures NAAQS attainment. 

In relation to whether the binned 

approach used for Seward’s RRE 

modeling provided adequate assurance 

that hourly emissions when in 

compliance with the longer term limit 

provided for attainment, EPA notes that 

the binned approach did not account for 

the 99th percentile of historic hourly 

data, nor did it provide evidence that an 

analysis based on a metric other than 

99th percentile of hourly emissions data 

could result in a comparably stringent 

longer term limit. This means that 

PADEP did not establish that the longer 

term limit for Seward was comparably 

stringent to an attaining 1-hour CEV, 

and that EPA erred in approving the 

attainment demonstration and limit as 

providing for NAAQS attainment. Thus, 

EPA is proposing to correct its prior 

approval to a disapproval of the 

attainment demonstration for Seward. 

D. RACM/RACT 

CAA section 172(c)(1) requires that 

each attainment plan provide for the 

implementation of all reasonably 

available control measures (i.e., RACM) 

as expeditiously as practicable and shall 

provide for attainment of the NAAQS. 

Section 172(c)(6) requires SIPs to 

contain enforceable emission limitations 

and control measures as may be 

necessary or appropriate to provide for 

NAAQS attainment. EPA interprets 

RACM, including RACT, under section 

172 as measures that a state determines 

to be both reasonably available and 

contribute to attainment as 

expeditiously as practicable ‘‘for 

existing sources in the area.’’ 

Pennsylvania’s October 11, 2017, 

submittal discusses Federal and state 

measures that Pennsylvania asserts will 

provide emission reductions leading to 

attainment and maintenance of the 2010 

SO2 NAAQS. With regard to state rules, 

Pennsylvania cites its low sulfur fuel 

rules, which were SIP-approved on July 

10, 2014 (79 FR 39330). Pennsylvania’s 

low sulfur fuel oil provisions apply to 

refineries, pipelines, terminals, retail 

outlet fuel storage facilities, commercial 

and industrial facilities, and facilities 

with units burning regulated fuel oil to 

produce electricity and domestic home 

heaters. These low sulfur fuel oil rules 

reduce the amount of sulfur in fuel oils 

used in combustion units, thereby 

reducing SO2 emissions and the 

formation of sulfates that cause 

decreased visibility. 

The October 11, 2017, submittal also 

discusses that the main SO2 emitting 

sources at Conemaugh, Homer City, 

Keystone, and Seward are all equipped 

with FGD systems (wet limestone 

scrubbers, dry FGD, or in-furnace 

limestone injection systems) to reduce 

SO2 emissions. Table 3 in this document 

lists the control technology at each of 


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the main SO2 emitting sources at each 

facility. 

TABLE 3—CONTROL TECHNOLOGY AT THE FOUR MAJOR SO2 SOURCES IN THE INDIANA AREA

Facility Unit SO2 control 

Control 

installation 

date 

Conemaugh ............................. 031—Main Boiler 1 ................. Wet limestone scrubber ........................................................... ∼1994 

031—Main Boiler 2 ................. Wet limestone scrubber ........................................................... ∼1995 

Homer City .............................. 031—Boiler 1 .......................... Dry FGD ................................................................................... 11/18/2015 

032—Boiler 2 .......................... Dry FGD ................................................................................... 5/23/2016 

033—Boiler 3 .......................... Wet limestone scrubber ........................................................... ∼2002 

Keystone .................................. 031—Boiler 1 .......................... Wet limestone scrubber ........................................................... 9/24/2009 

032—Boiler 2 .......................... Wet limestone scrubber ........................................................... 11/22/2009 

Seward .................................... 034—CFB Boiler 1 .................. In-furnace limestone injection .................................................. ∼2004 

035—CFB Boiler 2 .................. In-furnace limestone injection .................................................. ∼2004 

With these controls installed, the 

October 11, 2017, submittal discusses 

facility-specific control measures, 

namely SO2 emission limits for 

Conemaugh, Homer City, and Seward, 

and new SO2 emission limits for 

Keystone. Keystone’s new limits were 

developed through air dispersion 

modeling (default AERMOD as 

described below) submitted by PADEP. 

In order to ensure that the Indiana Area 

demonstrates attainment with the SO2

NAAQS, PADEP asserts that the 

following combination of emission 

limits at the four facilities is sufficient 

for the Indiana Area to meet the SO2

NAAQS and serve as RACM/RACT: 

• Conemaugh’s current SO2 emission 

limits contained in the Title V 

Operating Permit (TVOP) 32–00059 

because the emission limits for 

Conemaugh determined by the 

modeling as necessary for SO2

attainment would be less stringent; 

• Seward’s current SO2 emission 

limit in TVOP 32–00040 because the 

emission limits for Seward determined 

by the modeling as necessary for SO2

attainment would be less stringent; 

• Homer City’s current SO2 emission 

limits established in Plan Approval 32– 

00055H and Plan Approval 32–00055I; 

and 

• A new, more stringent combined 

SO2 emission limit for Keystone Unit 1 

and Unit 2 of 9,600 lbs/hr block 24-hour 

average limit. 

The emission limits for each of the SO2- 

emitting facilities are listed in Table 4 

in this document. 

TABLE 4—SO2 EMISSION LIMITS FOR INDIANA AREA FACILITIES

Facility Source description Emission limit 

(lbs/hr) Averaging period 

Conemaugh ......................... Unit 1 .................................

Unit 2 .................................

1,656 (TVOP 32–00059) ............................................... 3-hour block. 

Homer City ........................... Unit 1 .................................

Unit 2 .................................

Unit 3 .................................

6,360 (Plan Approval 32–00055H) and limits specified 

in Plan Approval 32–00055I.

1-hour block. 

Keystone .............................. Unit 1 .................................

Unit 2 .................................

9,600 (New limit based on default AERMOD) .............. 24-hour block. 

Seward ................................. Unit 1 .................................

Unit 2 .................................

3,038.4 (TVOP 32–00040) ............................................ 30-day rolling. 

The emission limits for Conemaugh, 

Keystone and Seward have averaging 

times greater than 1-hour (ranging 

between three hours and 30 days). The 

SO2 limits at Conemaugh are set to a 3- 

hour block average. This average is 

roughly in line with the CEV modeled 

limit and the ratio from Appendix C in 

EPA’s 2014 SO2 Nonattainment 

Guidance. Keystone’s limits were set to 

a 24-hour block average based on the 

100 RRE simulation method discussed 

in the Attainment Demonstration 

section in this proposed rulemaking. A 

similar approach was used to establish 

a 30-day rolling average for Seward. 

Appendices C–1a and C–4 of 

Pennsylvania’s October 11, 2017, SIP 

submittal, and the modeling report of 

the February 5, 2020, submittal, provide 

detailed explanation of the longer-term 

emission limits. 

EPA expects to consider the following 

factors in evaluating the adequacy of 

plans with limits based on longer 

averaging times: (l) Whether the 

numerical value of the mass emissions 

limit averaged over a longer time is 

comparably stringent to a 1-hour limit at 

the CEV; and (2) whether the longerterm average limit, potentially in 

combination with other limits, can be 

expected to constrain emissions 

sufficiently so that any occasions of 

emissions above the CEV will be limited 

in frequency and magnitude and, if they 

occur, would not be expected to result 

in NAAQS violations. 

EPA analyzed the last five years of 

emissions data for Keystone and Seward 

in order to understand the source’s 

historic emissions variability. EPA used 

the methodology described in Appendix 

C of the 2014 SO2 Nonattainment 

Guidance to calculate adjustment factors 

for each source. Refer to EPA’s TSD 

entitled Reconsideration of the 

Attainment Plan for the Indiana, PA 1- 

Hour SO2 Nonattainment Area (January 

2022) for a detailed description of EPA’s 

analysis. 

The 2014 SO2 Nonattainment 

Guidance recommends the use of a data 

set that reflects hourly data for at least 

3 to 5 years of stable operation (i.e., 

without changes that significantly alter 

emissions variability) to obtain a 

suitably reliable analysis. EPA analyzed 

two 3-year periods and one 5-year 

period for Keystone, and one 3-year 


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18SO2 Guideline Document, U.S. Environmental 

Protection Agency, Office of Air Quality Planning 

and Standards, Research Triangle Park, NC 27711, 

EPA–452/R–94–008, February 1994. Located at: 

https://www.epa.gov/ttn/oarpg/t1pgm.html. 

period and one 5-year period for Seward 

for illustrative purposes. Because the 

analyses for Seward and Keystone were 

done for illustrative purposes, the 

adjustment factors resulting from the 

analyses are also only for illustrative 

purposes. Using the current CEV for 

Keystone of 9,711 lb/hr, and depending 

upon the years of data used, Keystone’s 

24-hour block limits could be either 

8,573.0 lbs/hr, 8,959.5 lb/hr, or 8,225.3 

lbs/hr. Using Seward’s CEV determined 

by Pennsylvania’s supplemental 

analysis (4,500 lbs/hr) the 30-day rolling 

limit would be 3,484.3 lbs/hr using the 

3-year adjustment factor and 2,575.3 

lbs/hr using the 5-year adjustment 

factor. 

EPA compared these values to 

Pennsylvania’s RRE modeling derived 

24-hr limit for Keystone (9,600 lb/r) and 

the 30-day limit for Seward (3,038 lb/ 

hr). For Keystone, the comparably 

stringent values calculated by EPA are 

between 640 and 1,375 lb/hr less than 

the limit Pennsylvania claimed was 

protective of the standard, which was 

9,600 lb/hr on a 24-hour block basis. 

The significant difference between 

Pennsylvania’s RRE-derived 24-hour 

limit for Keystone and the potential 24- 

hour limits calculated by EPA using 

Appendix C of the 2014 SO2 Guidance 

calls into question whether Keystone’s 

RRE-derived 24-hour limit of 9,600 lb/ 

hr is comparably stringent to the 1-hr 

CEV. If the RRE-derived limit is not 

comparably stringent to the CEV that 

was modeled to show attainment of the 

SO2 NAAQS, then it is uncertain 

whether the longer-term 24-hour limit 

will provide for attainment of the 

NAAQS. 

For Seward, when using the last three 

years of available emissions data (2018– 

2020), EPA calculated 30-day emission 

limit following the Appendix C 

methodology is 446 lb/hr more than the 

adopted limit of 3,038 lb/hr. When 

using the last five years of available 

emissions data (2016–2020), EPA 

calculated 30-day limit is 463 lb/hr less 

than Seward’s current limit. The large 

difference in these 30-day limits 

probably results from the decrease in 

SO2 emission spikes at Seward, both in 

frequency and magnitude, that occurred 

after 2017. Seward’s SO2 emissions 

spikes have declined in magnitude and 

frequency over the last 3 years, which 

may be due to the operational changes 

referenced in the February 5, 2020, 

submittal. The 30-day average SO2 limit 

for Seward has been in place since 2001 

and has not been supplemented with 

additional limits to reflect the 

operational changes noted. As 

mentioned earlier in the preamble, EPA 

must consider whether the longer-term 

average limit can be expected to 

constrain emissions sufficiently so that 

emissions above the CEV will be limited 

in frequency and magnitude and, if they 

occur, would not be expected to result 

in NAAQS violations. Historic hourly 

emissions (described in the January 

2022 TSD) before 2018 show that it is 

possible for this source to be in 

compliance with the 30-day limit of 

3,038 lb/hr yet have up to 171 hours 

over the CEV. This data supports EPA’s 

earlier conclusion that the current limit, 

by itself, does not adequately constrain 

the frequency and magnitude of hourly 

exceedances of the CEV and is not 

comparably stringent to the CEV. 

As described earlier in the preamble, 

in EPA’s October 2020 final action on 

this attainment plan, EPA failed to 

consider a critical aspect of longer-term 

limits in relation to the 1-hour SO2

NAAQS, which was whether the longerterm limits for Keystone and Seward 

were comparably stringent to their CEVs 

and therefore support a conclusion that 

compliance with the longer term limits 

will provide for NAAQS attainment, 

which is necessary to meet the RACM/ 

RACT requirement under EPA’s SO2

policy. Absent a comparably stringent 

analysis from Pennsylvania, EPA is 

proposing that it erred in previously 

approving the RACM/RACT element for 

the Indiana Area SIP and proposes to 

change its prior approval of the RACM/ 

RACT element to a disapproval of the 

RACT/RACM element for Seward and 

Keystone. 

The emission limits of the four SIP 

sources and all related compliance 

parameters (i.e., the measures which 

include system audits, record-keeping 

and reporting, and corrective actions) 

have been incorporated into the SIP via 

EPA’s final approval of the Indiana, PA 

SO2 attainment plan (85 FR 66240, 

October 19, 2020) which made these 

changes federally enforceable. EPA is 

proposing to retain the emission limits 

and compliance parameters for the main 

sources of SO2 in the SIP as SIP 

strengthening measures while 

Pennsylvania works on revised limits 

for its attainment plan. Maintaining 

these limits and measures as SIP 

strengthening measures is appropriate 

for limits that improve air quality but do 

not meet a specific CAA requirement 

(see 86 FR 14827 at 14828, March 19, 

2021). 

E. RFP Plan 

Section 172(c)(2) of the CAA requires 

that an attainment plan include a 

demonstration that shows RFP for 

meeting air quality standards will be 

achieved through generally linear, 

incremental improvements in air 

quality. Section 171(1) of the CAA 

defines RFP as ‘‘such annual 

incremental reductions in emissions of 

the relevant air pollutant as are required 

by this part (part D) or may reasonably 

be required by EPA for the purpose of 

ensuring attainment of the applicable 

NAAQS by the applicable attainment 

date.’’ As stated originally in the 1994 

SO2 Guidelines Document 18 and 

repeated in the 2014 SO2 Nonattainment 

Guidance, EPA continues to believe that 

this definition is most appropriate for 

pollutants that are emitted from 

numerous and diverse sources, where 

the relationship between emissions from 

these numerous and diverse sources and 

the effect of those emissions on ambient 

air quality are difficult to ascertain. In 

such cases, emissions reductions may be 

required from numerous and varying 

types of sources in numerous locations. 

The relationship between ambient SO2

concentrations and the sources of SO2

emissions is much more discernable and 

definable. That is, it is easier to 

determine the effect on ambient SO2

concentrations that SO2 emission 

reductions from certain sources will 

produce. Moreover, the emissions 

reductions from these few sources 

necessary to attain the SO2 NAAQS 

usually occur in one step, which often 

(but not always) results from installation 

of new or better controls on a few 

sources that represent a knowable, 

specific amount of SO2 reductions, 

rather than the piecemeal and gradual 

adoption of controls or measures by 

numerous sources. Therefore, EPA 

interpreted RFP for SO2 as adherence to 

an ambitious compliance schedule for 

the adoption of controls or newer limits 

on these SO2 sources in both the 1994 

SO2 Guideline Document and the 2014 

SO2 Nonattainment Guidance. 

The purpose of an ambitious 

compliance schedule is to ensure that 

SO2 sources reach the SO2 emission 

limits that were modeled to show 

attainment as soon as possible, but no 

later than the compliance date. If the 

emission limits themselves have not 

been shown to model attainment, then 

an ambitious compliance schedule will 

not necessarily result in attainment, and 

reasonable further progress toward 

attainment may not lead to attainment. 

As noted, on reconsideration EPA does 

not view the longer term emission limits 

derived by Pennsylvania using RRE 

modeling to be comparably stringent to 

the CEVs used in the modeling that 


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19 In the Round 3 intended designations (82 FR 

41903) published September 5, 2017, EPA endorsed 

a value of 196.4 mg/m3 (based on calculations using 

all available significant figures) as equivalent to the 

2010 SO2 standard. To avoid confusion, EPA is 

Continued 

demonstrated future attainment of the 

NAAQS. Therefore, EPA finds there is a 

lack of evidence showing that these 

longer term limits will yield a sufficient 

reduction in SO2 emissions in the 

Indiana NAA to attain the NAAQS. As 

a result, EPA is proposing to determine 

that Pennsylvania’s SO2 attainment plan 

for the Indiana Area is not adequate to 

achieve attainment of the NAAQS 

because the RRE-derived longer term 

limits have not been adequately shown 

to provide for sufficient SO2 emission 

reductions in the Indiana Area. Without 

this assurance, EPA is proposing to 

determine that it erred in previously 

approving the RFP element of 

Pennsylvania’s SO2 attainment plan for 

the Indiana Area. EPA proposes to 

change its prior approval of the RFP 

element to a disapproval of 

Pennsylvania’s attainment plan with 

respect to the RFP requirements. 

F. Contingency Measures 

In accordance with section 172(c)(9) 

of the CAA, contingency measures are 

required as additional measures to be 

implemented in the event that an area 

fails to meet the RFP requirements or 

fails to attain the standard by its 

attainment date. These measures must 

be fully adopted rules or control 

measures that can be implemented 

quickly and without additional EPA or 

state action if the area fails to meet RFP 

requirements or fails to meet its 

attainment date and should contain 

trigger mechanisms and an 

implementation schedule. However, 

SO2 presents special considerations. As 

stated in the final 2010 SO2 NAAQS 

promulgation on June 22, 2010 (75 FR 

35520), and in the 2014 SO2

Nonattainment Guidance, EPA 

explained that because of the 

quantifiable relationship between SO2

sources and control measures, provided 

that the attainment plan demonstrates 

that emissions performance under the 

allowable emissions limits in the SIP 

provide for NAAQS attainment, it is 

appropriate that state agencies develop 

a comprehensive program to identify 

sources of violations of the SO2 NAAQS 

and undertake an aggressive follow-up 

for compliance and enforcement of 

those emission limits. 

The Consent Order and Agreements 

(COAs) or Consent Orders (COs) for 

Conemaugh, Homer City, Keystone, and 

Seward (see Appendices B–1 through 

B–4 of the October 11, 2017 submittal 

and updated permits submitted on 

February 5, 2020) each contain the 

following measures that are designed to 

keep the Indiana Area from triggering an 

exceedance or violation of the SO2

NAAQS: (1) Upon execution of the COA 

or CO, if SO2 emissions from the 

combined SO2 emitting sources at the 

facility exceed 99% of the SO2

emissions limit for the facility, within 

48 hours the facility is required to 

undertake a full system audit of the SO2

emitting sources and submit a written 

report to PADEP within 15 days, and 

corrective actions shall be identified by 

PADEP as necessary; and (2) upon 

execution of the COA or CO, if the 

Strongstown monitor (ID 42–063–0004) 

measures a 1-hour concentration 

exceeding 75 ppb, PADEP will notify 

the facility in the NAA, and the facility 

is required to identify whether any of 

the SO2-emitting sources at the 

respective facility were running at the 

time of the exceedance, and within a 

reasonable time period leading up to the 

exceedance, not to exceed 24 hours. If 

any of the SO2-emitting sources were 

running at the time of the exceedance, 

the facility must then analyze the 

meteorological data on the day the daily 

exceedance occurred to ensure that the 

daily exceedance was not due to SO2

emissions from the respective facility. 

The facility’s findings must be 

submitted to PADEP within 30 days of 

being notified of the exceedance. 

Additionally, if PADEP identifies a 

daily maximum SO2 concentration 

exceeding 75 ppb at a PADEP-operated 

SO2 ambient air quality monitor in the 

Indiana Area, within 5 days, PADEP 

will contact Conemaugh, Homer City, 

Keystone, and Seward to trigger the 

implementation of the daily exceedance 

report contingency measure described 

in section VIII.C. of the October 11, 

2017, submittal. If necessary, section 

4(27) of the Pennsylvania Air Pollution 

Control Act (APCA) authorizes PADEP 

to take any action it deems necessary or 

proper for the effective enforcement of 

APCA and the rules and regulations 

promulgated under APCA. Such actions 

include the issuance of orders and the 

assessment of civil penalties. A more 

detailed description of the contingency 

measures can be found in section VIII of 

the October 11, 2017, submittal as well 

as the COAs and COs included in the 

submittal and included for 

incorporation by reference into the SIP. 

EPA is proposing to change its prior 

finding that Pennsylvania’s October 11, 

2017 and February 5, 2020 submittals 

include sufficient contingency 

measures, since EPA is now proposing 

that they are based on the emission 

limits, including longer term emission 

limits, that on reconsideration EPA 

believes have not been shown as 

comparably stringent to the CEVs used 

in the modeling that demonstrated 

attainment and consequently cannot 

support a conclusion that compliance 

with the allowable limits in the 

attainment plan will provide for 

NAAQS attainment. Therefore, on 

reconsideration EPA proposes that it 

erred in previously approving the 

contingency measures submitted by 

Pennsylvania, and now proposes to 

correct this error by proposing to change 

its approval of this element to 

disapproval because they do not follow 

the 2014 SO2 Nonattainment Guidance 

and do not meet the section 172(c)(9) 

requirements. Nevertheless, EPA is 

proposing to retain the contingency 

measures in the SIP which were 

approved into the SIP on October 19, 

2020 (85 FR 66240), as SIP 

strengthening measures. Specific 

needed amendments to the contingency 

measures can be evaluated and 

determined in the context of developing 

a new attainment plan that 

appropriately demonstrates that its 

emission limits and control measures 

will provide for NAAQS attainment. 

III. Summary of Sierra Club Modeling 

Analysis for Westmoreland and 

Cambria Counties Submitted During the 

Public Comment Period (83 FR 32606, 

July 13, 2018) and EPA Considerations 

A. Modeled Violations in Westmoreland 

and Cambria Counties 

During the public comment period for 

the proposed approval of this 

attainment plan (83 FR 32606, July 13, 

2018), the Sierra Club (in conjunction 

with the National Parks Conservation 

Association, PennFuture, Earthjustice, 

and Clean Air Council) submitted a 

modeling analysis using actual 

emissions and the CEVs for Conemaugh 

and Seward which claimed to show 

violations of the SO2 NAAQS outside of 

the nonattainment area, beyond the 

eastern border of Indiana county within 

nearby portions of Westmoreland and 

Cambria counties. The modeling used 

the same meteorological data, stack 

parameters, background concentrations 

and building downwash as 

Pennsylvania’s October 11, 2017, 

submittal. The Sierra Club modeling 

used emission inputs of actual historical 

emissions (2013- 2018 quarter 1) and a 

finer receptor grid that included 

receptors outside Indiana County. When 

modeling 2015–2017 emissions, the 

resulting design value was 293.4 ug/m3, 

and when modeling 2013–2017 

emissions, the resulting design value 

was 267.2 ug/m3.19 The comment letter 


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expecting attainment demonstrations to show 

achievement with concentrations at or below 

precisely 196.4 mg/m3. 

20On April 7, 2021, the Administrator directed all 

EPA offices to take immediate and affirmative steps 

to incorporate EJ considerations into their work, 

including assessing impacts to pollution-burdened, 

underserved, and Tribal communities in regulatory 

development processes and considering regulatory 

options to maximize benefits to these communities. 

Message from the EPA Administrator, Our 

Commitment to Environmental Justice (issued April 

7, 2021) at https://www.epa.gov/sites/production/ 

files/2021-04/documents/regan-messageon

commitmenttoenvironmentaljusticeapril072021.pdf; ‘‘Executive Order on Advancing 

Racial Equity and Support for Underserved 

Communities Through the Federal Government’’ 

(E.O. 13985, issued January 20, 2021) at https://

www.whitehouse.gov/briefing-room/presidentialactions/2021/01/20/executive-order-advancingracial-equity-and-support-for-underservedcommunities-through-the-federal-government/ and 

86 FR 7009 (January 25, 2021). 

21See https://www.epa.gov/environmentaljustice/ 

learn-about-environmental-justice. 

and modeling results can be found in 

the Docket for this action. 

Under reconsideration, EPA notes that 

Sierra Club’s modeling, using actual 

emissions and the CEVs for Conemaugh 

and Seward, although using slightly 

different data from PA’s modeling, 

suggests that there are modeled SO2

nonattainment violations outside the 

NAA, and nothing in PA’s submittal 

rebuts the finding of nonattainment 

outside the NAA. 

As stated in the October 2020 final 

rule action, although EPA does not 

consider that a failure to include an 

analysis of modeled SO2 concentrations 

outside of the boundaries of the NAA is 

an independent basis on which to 

disapprove this attainment plan, EPA is 

now proposing to revise its prior full 

approval of the attainment plan to a 

partial disapproval in order to correct 

errors made in approving the attainment 

demonstration, and the RACM/RACT, 

RFP and contingency measure elements. 

EPA encourages the state, when 

developing a new attainment plan that 

would respond to this partial 

disapproval, if finalized, to additionally 

ensure that any revised attainment plan 

demonstrates attainment for all known 

modeled violations. EPA is also 

considering taking a separate statutory 

action under the Clean Air Act to 

address the modeled violations in 

Westmoreland and Cambria counties. 

B. Environmental Justice Considerations 

EPA conducted an environmental 

justice (EJ) analysis on the Indiana NAA 

and Westmoreland and Cambria 

counties. The consideration of 

environmental justice concerns is 

consistent with the EPA Administrator’s 

directive and presidential executive 

orders.20 The EPA has defined 

environmental justice as ‘‘the fair 

treatment and meaningful involvement 

of all people regardless of race, color, 

national origin, or income with respect 

to the development, implementation 

and enforcement of environmental laws, 

regulations and policies.’’ 21 A detailed 

description of the EJ analysis is 

available in the TSD for this action, 

which can be found under Docket ID 

No. EPA–R03–OAR–2017–0615 and 

online at www.regulations.gov. 

Vulnerable populations (characterized 

by the low-income criteria as discussed 

in the TSD) are found inside and 

outside the SO2 nonattainment area 

boundary. In particular, the areas 

identified by the Sierra Club modeling 

outside the NAA in Westmoreland and 

Cambria counties are also identified as 

vulnerable populations. EPA 

recommends that Pennsylvania’s 

response to our action, if finalized, 

should be as expeditious as practicable 

and take into account the emissions 

impact on the vulnerable populations 

both inside the current nonattainment 

area, and in adjacent areas. EPA is 

committed to environmental justice for 

all people and expects PADEP in its 

CAA obligations to ensure that public 

health protection of all people in the 

Commonwealth is consistent with both 

EPA’s and PADEP’s commitments. 

IV. Proposed Action 

EPA is proposing to amend its prior 

full approval of the Indiana Area SO2

attainment plan to a partial approval 

and partial disapproval. Specifically, 

EPA is proposing to retain approval of 

the emissions inventory and NNSR 

elements of Pennsylvania SIP revision 

and disapprove the attainment plan, 

RACM/RACT demonstration, RFP 

element, and contingency measures 

which were submitted on October 11, 

2017, and February 5, 2020. EPA is 

soliciting public comments on the 

issues discussed in this document. 

These comments will be considered 

before taking final action. 

V. Incorporation by Reference 

In this document, EPA is proposing to 

include in a final EPA rule regulatory 

text that includes incorporation by 

reference. In accordance with 

requirements of 1 CFR 51.5, EPA is 

proposing to retain the following 

information as SIP strengthening 

measures. These measures were 

incorporated by reference into the SIP 

under the approval of this attainment 

plan (85 FR 66240, October 19, 2020). If 

this proposed disapproval is finalized, 

EPA does not intend to remove these 

measures, but to retain them. The 

measures are: The portions of the COAs 

or COs entered between Pennsylvania 

and Conemaugh, Homer City, Keystone, 

and Seward that are not redacted, as 

well as the unredacted portions of the 

TVOPs or Plan Approval included in 

the October 11, 2017 submittal and the 

corrected documents in the February 5, 

2020 submittal. These include emission 

limits and associated compliance 

parameters (i.e., the measures which 

include system audits, record-keeping 

and reporting, and corrective actions). 

EPA has made, and will continue to 

make, these materials generally 

available through https://

www.regulations.gov and at the EPA 

Region III Office (please contact the 

person identified in the FOR FURTHER

INFORMATION CONTACT section of this 

preamble for more information). 

VI. Statutory and Executive Order 

Reviews 

Executive Orders 12866 and 13563: 

Regulatory Planning and Review 

Under Executive Orders 12866 (58 FR 

51735, October 4, 1993) and 13563 (76 

FR 3821, January 21, 2011), this action 

is not a ‘‘significant regulatory action’’ 

and, therefore, is not subject to review 

by the Office of Management and 

Budget. 

Executive Order 13771: Reducing 

Regulations and Controlling Regulatory 

Costs 

This action is not an Executive Order 

13771 regulatory action because this 

action is not significant under Executive 

Order 12866. 

Paperwork Reduction Act 

This rulemaking does not impose an 

information collection burden under the 

provisions of the Paperwork Reduction 

Act of 1995 (44 U.S.C. 3501 et seq.). 

Regulatory Flexibility Act 

This action merely proposes to 

disapprove state requirements as not 

meeting Federal requirements and 

imposes no additional requirements 

beyond those imposed by state law. 

Accordingly, the Administrator certifies 

that this rulemaking will not have a 

significant economic impact on a 

substantial number of small entities 

under the Regulatory Flexibility Act (5 

U.S.C. 601 et seq.). 

Unfunded Mandates Reform Act 

Because this rulemaking proposes to 

disapprove pre-existing requirements 

under state law and does not impose 

any additional enforceable duty beyond 

that required by state law, it does not 

contain any unfunded mandate or 

significantly or uniquely affect small 


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Federal Register / Vol. 87, No. 52 / Thursday, March 17, 2022 / Proposed Rules 15179 

governments, as described in the 

Unfunded Mandates Reform Act of 1995 

(Pub. L. 104–4). 

Executive Order 13132: Federalism 

This action also does not have 

federalism implications because it does 

not have substantial direct effects on the 

states, on the relationship between the 

National Government and the states, or 

on the distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132 (64 FR 43255, 

August 10, 1999). This action merely 

proposes to disapprove a state 

requirement and does not alter the 

relationship or the distribution of power 

and responsibilities established in the 

CAA. 

Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

In addition, the SIP is not approved 

to apply on any Indian reservation land 

or in any other area where EPA or an 

Indian tribe has demonstrated that a 

tribe has jurisdiction. In those areas of 

Indian country, the rulemaking does not 

have tribal implications and will not 

impose substantial direct costs on tribal 

governments or preempt tribal law as 

specified by Executive Order 13175 (65 

FR 67249, November 9, 2000). 

Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

This rulemaking also is not subject to 

Executive Order 13045 ‘‘Protection of 

Children from Environmental Health 

Risks and Safety Risks’’ (62 FR 19885, 

April 23, 1997), because it proposes to 

disapprove a state rule. 

Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution, or Use 

Because it is not a ‘‘significant 

regulatory action’’ under Executive 

Order 12866 or a ‘‘significant energy 

action,’’ this action is also not subject to 

Executive Order 13211 (66 FR 28355, 

May 22, 2001). 

National Technology Transfer 

Advancement Act 

In reviewing state submissions, EPA’s 

role is to approve state choices, 

provided that they meet the criteria of 

the CAA. In this context, in the absence 

of a prior existing requirement for the 

state to use voluntary consensus 

standards (VCS), EPA has no authority 

to disapprove a state submission for 

failure to use VCS. It would thus be 

inconsistent with applicable law for 

EPA, when it reviews a state 

submission, to use VCS in place of a 

state submission that otherwise satisfies 

the provisions of the CAA. Thus, the 

requirements of section 12(d) of the 

National Technology Transfer and 

Advancement Act of 1995 (15 U.S.C. 

272 note) do not apply. 

Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

Executive Order 12898 (59 FR 7629 

(February 16, 1994)) establishes Federal 

executive policy on environmental 

justice. Its main provision directs 

Federal agencies, to the greatest extent 

practicable and permitted by law, to 

make environmental justice part of their 

mission by identifying and addressing, 

as appropriate, disproportionately high 

and adverse human health or 

environmental effects of their programs, 

policies, and activities on minority 

populations and low-income 

populations in the United States. EPA 

lacks the discretionary authority to 

address environmental justice in this 

action. In reviewing SIP submissions, 

EPA’s role is to approve or disapprove 

state choices, based on the criteria of the 

CAA. 

Accordingly, this action proposing 

partial disapproval of Pennsylvania’s 

SO2 attainment plan for the Indiana 

Area, merely disapproves certain state 

requirements and retains certain state 

requirements as SIP strengthening 

measures in the SIP under section 110 

of the CAA and will not in-and-of itself 

create any new requirements. 

Accordingly, it does not provide EPA 

with the discretionary authority to 

address, as appropriate, 

disproportionate human health or 

environmental effects, using practicable 

and legally permissible methods, under 

Executive Order 12898. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Reporting and recordkeeping 

requirements, Sulfur oxides. 

Dated: March 8, 2022. 

Diana Esher, 

Acting Regional Administrator, Region III. 

[FR Doc. 2022–05398 Filed 3–16–22; 8:45 am] 

BILLING CODE 6560–50–P 

FEDERAL MARITIME COMMISSION 

46 CFR Chapter IV 

[Docket No. 22–04] 

RIN 3072–AC90 

Demurrage and Detention Billing 

Requirements 

AGENCY: Federal Maritime Commission. 

ACTION: Advance notice of proposed 

rulemaking; Extension of comment 

period. 

SUMMARY: The Federal Maritime 

Commission (Commission) is extending 

the deadline for the submission of 

public comments in response to its 

February 15, 2022, Advance Notice of 

Proposed Rulemaking on demurrage and 

detention billing requirements. The 

Commission grants the request by a 

coalition of associations seeking a 30- 

day extension to the comment period. 

DATES: The comments due date for the 

advance notice of proposed rulemaking 

published February 15, 2022, at 87 FR 

8506 is extended. Submit comments on 

or before April 16, 2022. 

ADDRESSES: You may submit comments, 

identified by Docket No. 22–04, by 

email at secretary@fmc.gov. For 

comments, include in the subject line: 

‘‘Docket No. 22–04, Comments on 

Demurrage and Detention Billing 

Requirements ANPRM.’’ Comments 

should be attached to the email as a 

Microsoft Word or text-searchable PDF 

document. Only non-confidential and 

public versions of confidential 

comments should be submitted by 

email. 

Instructions: For detailed instructions 

on submitting comments, including 

requesting confidential treatment of 

comments, and additional information 

on the rulemaking process, see the 

Public Participation heading of the 

Supplementary Information section of 

this document. Note that all comments 

received will be posted without change 

to the Commission’s website unless the 

commenter has requested confidential 

treatment. 

Docket: For access to the docket to 

read background documents or 

comments received, go to the 

Commission’s Electronic Reading Room 

at: https://www2.fmc.gov/readingroom/ 

proceeding/22-04. 

FOR FURTHER INFORMATION CONTACT: 

William Cody, Secretary; Phone: (202) 

523–5725; Email: secretary@fmc.gov. 

SUPPLEMENTARY INFORMATION: 


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