46434 Federal Register / Vol. 82, No. 192 / Thursday, October 5, 2017 / Proposed Rules 

1 Illinois’ final rule amended other state 

regulations that are not part of Illinois’ 

nonattainment plans for the 2010 SO2 NAAQS and 

were not submitted to EPA as part of this action. 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R05–OAR–2016–0138; FRL–9968–84- 

Region 5] 

Air Plan Approval; Illinois; 

Nonattainment Plans for the Lemont 

and Pekin SO2 Nonattainment Areas 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to approve 

State Implementation Plan (SIP) 

revisions, which Illinois submitted to 

EPA on March 2, 2016, and 

supplemented on August 8, 2016 and 

May 4, 2017, for attaining the 2010 1- 

hour sulfur dioxide (SO2) national 

ambient air quality standard (NAAQS) 

for the Lemont and Pekin areas. These 

revisions (herein called the 

nonattainment plans or plans) include 

Illinois’ attainment demonstration and 

other elements required under Clean Air 

Act (CAA) for the two areas. In addition 

to an attainment demonstration, the 

plans address: The requirement for 

meeting reasonable further progress 

(RFP) toward attainment of the NAAQS; 

reasonably available control measures 

and reasonably available control 

technology (RACM/RACT); emission 

inventories; and contingency measures. 

EPA further proposes to conclude that 

Illinois has demonstrated that the plans’ 

provisions provide for attainment of the 

2010 1-hour primary SO2 NAAQS in the 

Lemont and Pekin areas by the 

attainment date of October 4, 2018. 

DATES: Comments must be received on 

or before November 6, 2017. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R05– 

OAR–2016–0138 at http://

www.regulations.gov, or via email to 

aburano.douglas@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 

http://www2.epa.gov/dockets/ 

commenting-epa-dockets. 

FOR FURTHER INFORMATION CONTACT: John 

Summerhays, Environmental Scientist, 

Attainment Planning and Maintenance 

Section, Air Programs Branch (AR–18J), 

Environmental Protection Agency, 

Region 5, 77 West Jackson Boulevard, 

Chicago, Illinois 60604, (312) 886–6067, 

summerhays.john@epa.gov. 

SUPPLEMENTARY INFORMATION: 

This supplementary information 

section is arranged as follows: 

I. Why was Illinois required to submit SO2

plans for the Lemont and Pekin areas? 

II. Requirements for SO2 Nonattainment Area 

Plans 

III. Modeled Attainment Plans 

IV. Review of Residual and Distillate Fuel Oil 

Sulfur Content Limits 

V. Review of Other Plan Requirements 

VI. EPA’s Proposed Action 

VII. Incorporation by Reference 

VIII. Statutory and Executive Order Reviews 

I. Why was Illinois required to submit 

SO2 plans for the Lemont and Pekin 

areas? 

On June 22, 2010, EPA promulgated a 

new 1-hour primary SO2 NAAQS of 75 

parts per billion (ppb), which is met at 

an ambient air quality monitoring site 

when the 3-year average of the annual 

99th percentile of 1-hour daily 

maximum concentrations does not 

exceed 75 ppb, as determined in 

accordance with appendix T of 40 CFR 

part 50. See 75 FR 35520, codified at 40 

CFR 50.17(a)–(b). On August 5, 2013, 

EPA designated a first set of 29 areas of 

the country as nonattainment for the 

2010 SO2 NAAQS, including the 

Lemont and Pekin areas within Illinois. 

See 78 FR 47191, codified at 40 CFR 

part 81, subpart C. These area 

designations were effective October 4, 

2013. Section 191 of the CAA directs 

states to submit SIPs for areas 

designated as nonattainment (also 

referred to as nonattainment plans or 

plans) for the SO2 NAAQS to EPA 

within 18 months of the effective date 

of the designation, i.e., by no later than 

April 4, 2015, in this case. These plans 

are required to demonstrate that their 

respective areas will attain the NAAQS 

as expeditiously as practicable, but no 

later than five years from the effective 

date of designation, which in this case 

is October 4, 2018. 

For a number of areas, EPA published 

notice on March 18, 2016, that the 

pertinent states had failed to submit the 

required SO2 nonattainment plan by the 

18-month submittal deadline. See 81 FR 

14736. However, because Illinois had 

submitted its SO2 nonattainment plans 

before that date, EPA did not make such 

a finding with respect to the Lemont 

and Pekin areas. 

Illinois submitted nonattainment 

plans for the Lemont and Pekin areas on 

March 2, 2016 and submitted 

supplemental information on August 8, 

2016 and May 4, 2017.1 The remainder 

of this proposed rule describes the 

requirements that nonattainment plans 

must meet in order to obtain EPA 

approval, provides a review of the 

state’s plan with respect to these 

requirements, and describes EPA’s 

proposed action on the state’s plans. 

II. Requirements for SO2

Nonattainment Area Plans 

Nonattainment plans must meet the 

applicable requirements of the CAA, 

specifically CAA sections 172, 191 and 

192. On April 23, 2014, EPA issued 

guidance for meeting these statutory 

requirements, in a document entitled, 

‘‘Guidance for 1-Hour SO2

Nonattainment Area SIP Submissions,’’ 

(2014 SO2 Guidance) available at 

https://www.epa.gov/sites/production/ 

files/2016–06/documents/ 

20140423guidance_nonattainment_

sip.pdf. In the 2014 SO2 Guidance, EPA 

described the statutory requirements for 

a complete nonattainment area SIP 

under the 2010 SO2 NAAQS, which 

includes: An accurate emissions 

inventory of current emissions for all 

sources of SO2 within the 

nonattainment area; an attainment 

demonstration; demonstration of RFP; 

implementation of RACM (including 

RACT); a new source review (NSR) 

permit program; and adequate 

contingency measures for the affected 

area. 

In order for EPA to fully approve a 

SIP as meeting the requirements of CAA 

sections 172, 191 and 192, the SIP for 

the affected area must demonstrate, to 

EPA’s satisfaction, that each of the 

aforementioned requirements are met. 

In addition, the SIP must meet the 

applicable regulatory procedural and 

substantive requirements set forth in 

EPA’s regulations at 40 CFR part 51. 

Under CAA sections 110(l) and 193, 


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2An ‘‘average year’’ is used to mean a year with 

average air quality. While 40 CFR 50 appendix T 

provides for averaging three years of 99th percentile 

daily maximum values (e.g., the fourth highest 

maximum daily 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. 

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 that is 

a nonattainment area for any air 

pollutant may be modified in any 

manner unless it insures equivalent or 

greater emission reductions of such air 

pollutant. 

A. Emissions Inventory 

As required under CAA section 

172(c)(3), the state must develop and 

submit a comprehensive, accurate and 

current inventory of actual emissions 

from all sources of SO2 emissions in 

each nonattainment area. This inventory 

should be consistent with EPA’s most 

recent emissions inventory data 

requirements as codified at 40 CFR part 

51, subpart A. The emissions inventory 

serves as the foundation for modeling 

and other analyses that enable states to: 

(1) Estimate the degree to which 

different sources within a 

nonattainment area contribute to 

violations within the affected area; (2) 

assess the expected improvement in air 

quality within the nonattainment area 

due to the adoption and implementation 

of control measures; and ultimately 3) 

demonstrate that the adopted control 

measures provide for attainment of the 

SO2 standard by the attainment date. 

B. Attainment Plan 

CAA section 172(c)(1) directs states 

with areas designated as nonattainment 

to demonstrate that the submitted plan 

provides for attainment of the NAAQS. 

40 CFR part 51, subpart G further 

delineates the control strategy 

requirements that SIPs must meet. SO2

nonattainment 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 

that meets the requirements of 40 CFR 

part 51, appendix W which 

demonstrates that these emission limits 

and control measures provide for timely 

attainment of the SO2 NAAQS as 

expeditiously as practicable, but by no 

later than the attainment date for the 

affected area. The 2014 SO2 Guidance 

advises that compliance deadlines for 

these emission limits should be by, or 

before, January 1, 2017, in order to 

provide for air quality data at or below 

the level of the standard for at least one 

full calendar year before the attainment 

deadline. In cases where the necessary 

emission limits have not previously 

been made a part of the SIP, or have not 

otherwise become federally enforceable, 

the plan needs to include the necessary 

enforceable limits in adopted form 

suitable for incorporation into the SIP in 

order for it to be approved by EPA. 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 fully 

enforceable. 

The 2014 SO2 Guidance recommends 

that the emission limits be expressed as 

short-term average limits not to exceed 

the averaging time for the applicable 

NAAQS that the limit is intended to 

help maintain (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 guidance, pp. 22 

to 39. The guidance recommends that— 

should states utilize longer averaging 

times for certain sources—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 shown to 

provide for attainment. 

The 2014 SO2 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 conclusion, EPA considered the 

nature of the standard, conducted 

detailed analyses of the impact of use 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 to 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 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 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 EPA’s 

review of how to determine 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 nonattainment plans based 

on 1-hour emission limits, the standard 

approach is to conduct modeling using 

fixed emission rates. The maximum 

emission rate that would be modeled to 

result in attainment (i.e., the emission 

rate at which an ‘‘average year’’ 2 shows 

only three, not four days with maximum 

hourly levels exceeding 75 ppb) is 

labeled the ‘‘critical emission value.’’ 

The modeling process for identifying 

the critical emissions value 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 at this critical emission 

value. 

EPA recognizes that some sources 

have highly variable emissions due to, 

for example, 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 critical emission 

value. EPA also acknowledges the 

concern that longer term emission limits 

may allow short periods with emissions 

above the critical emissions value, 

which in turn would create the 

possibility of a NAAQS exceedance 

occurring when it otherwise would not 

if emissions were continuously 

controlled at the level corresponding to 

the critical emission value. However, for 

several reasons, EPA believes that the 

approach set forth in the 2014 SO2

Guidance addresses this concern. First, 


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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 the Agency 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 critical emissions value) and that 

takes the source’s emissions profile into 

account. As a result, EPA expects either 

form of emission limit to yield 

comparable air quality when the 

guidance is followed. 

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 

critical emission level, and in the longer 

term average limit scenario, the source 

is presumed occasionally to emit more 

than the critical emission value but on 

average, and presumably at most times, 

to emit well below the critical emission 

value. In an ‘‘average year,’’ 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 critical emission 

value 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 

longer term limit requires lower 

emissions most of the time because the 

limit is set well below the critical 

emission value, 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. 

As a hypothetical example to 

illustrate these points, suppose a source 

always emits 1000 pounds of SO2 per 

hour, which causes air quality to be at 

the level of the NAAQS (i.e., causes a 

design value of 75 ppb). Suppose further 

that in an ‘‘average year,’’ these 

emissions cause the five highest 

maximum daily average 1-hour 

concentrations to be 100 ppb, 90 ppb, 80 

ppb, 75 ppb, and 70 ppb. Then suppose 

that the source becomes subject to a 30- 

day average emission limit of 700 

pounds per hour. It is theoretically 

possible for a source meeting this limit 

to have emissions that occasionally 

exceed 1000 pounds per hour, but with 

a typical emissions profile emissions 

would much more commonly be 

between 600 and 800 pounds per hour. 

In this simplified example, assume a 

zero background concentration, which 

allows one to assume a linear 

relationship between emissions and air 

quality. (A nonzero background 

concentration would make the 

mathematics more difficult but would 

give similar results.) Air quality will 

depend on what emissions happen on 

what critical hours, but suppose that 

emissions on these 5 days are 800 

pounds per hour, 1100 pounds per hour, 

500 pounds per hour, 900 pounds per 

hour, and 1200 pounds per hour, 

respectively. This is a conservative 

example because the average of these 

emissions, 900 pounds per hour, is well 

over the 30-day average emission limit. 

These emissions would result in daily 

maximum 1-hour concentrations of 80 

ppb, 99 ppb, 40 ppb, 67.5 ppb, and 84 

ppb. In this example, the fifth day 

would have an exceedance that would 

not otherwise have occurred, but the 

third and fourth days would not have 

exceedances that otherwise would have 

occurred. In this example, the fourth 

highest maximum daily concentration 

under the 30-day average would be 67.5 

ppb. 

This simplified example illustrates 

the findings of a more complicated 

statistical analysis that EPA conducted 

using a range of scenarios using actual 

plant data. As described in appendix B 

of EPA’s 2014 SO2 Guidance, EPA found 

that the requirement for lower average 

emissions is highly likely to yield better 

air quality than is required with a 

comparably stringent 1-hour limit. 

Based on analyses described in 

appendix B of the 2014 SO2 Guidance, 

EPA has concluded 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 critical emission value. 

EPA must then evaluate whether this 

approach—which is likely to produce a 

lower number of overall exceedances 

even though it may produce some 

unexpected exceedances above the 

critical emission value—meets the 

requirement in section 110(a)(1) and 

172(c)(1) for state implementation plans 

to ‘‘provide for attainment’’ of the 

NAAQS. For SO2, as for other 

pollutants, it is generally impossible to 

design a nonattainment plan in the 

present that will guarantee that 

attainment will occur in the future. A 

variety of factors can cause a welldesigned attainment plan to fail and 

unexpectedly not result in attainment, 

for example if meteorology occurs that 

is more conducive to poor air quality 

than was anticipated in the plan. 

Therefore, in determining whether a 

plan meets the requirement to provide 

for attainment, EPA’s task is commonly 

to determine not whether the plan 

provides absolute certainty that 

attainment will in fact occur, but rather 

whether the plan provides an adequate 

level of confidence of prospective 

NAAQS attainment. From this 

perspective, in evaluating use of a 30- 

day average limit, EPA must weigh the 

likely net effect on air quality. Such an 

evaluation must consider the risk that 

occasions with meteorology conducive 

to high concentrations will have 

elevated emissions leading to 

exceedances that would not otherwise 

have occurred, and must also weigh the 

likelihood that the requirement for 

lower emissions on average will result 

in days not having exceedances that 

would have been expected with 

emissions at the critical emissions 

value. Additional policy considerations, 

such as the desirability of 

accommodating real world emissions 

variability without significant risk of 

violations as in this case, are also 

appropriate factors for EPA to weigh in 

determining whether there is a 

reasonable degree of confidence that the 

plan will lead to attainment. Based on 

these considerations, especially given 

the high likelihood that a limit averaged 

over as long as 30 days, determined in 

accordance with EPA’s guidance, 

should result in attainment, EPA 

believes as a general matter that such 

limits, if appropriately determined, can 

reasonably be considered to provide for 

attainment of the 2010 SO2 NAAQS. 

The 2014 SO2 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 critical emission value), 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 


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3For example, if the critical emission value 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. 

4EPA published revisions to the Guideline on Air 

Quality Models on January 17, 2017. 

5See section 110(a)(2)(A) of the CAA. 

6Section 172(c)(1) of the CAA provides that 

‘‘Such plan shall provide for the implementation of 

all reasonably available control measures as 

expeditiously as practicable (including such 

reductions in emissions from existing sources in the 

area as may be obtained through the adoption, at 

a minimum, of reasonably available control 

technology) and shall provide for attainment of the 

national primary ambient air quality standards.’’ 

7The annual and 24-hour primary SO2 NAAQS 

generally will remain in effect for 1 year following 

the effective date of the initial area designations for 

the new 1-hour 2010 SO2 NAAQS. However, the 

annual and/or 24-hour SO2 NAAQS will remain in 

place for a longer period of time for any current 

nonattainment area for the annual or 24-hour SO2

NAAQS, and any area for which a state has not 

fulfilled the requirements for a SIP call. See 40 CFR 

50.4(e). 

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, calculated according to the 

averaging time and averaging 

procedures of the prospective emission 

limitation. 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 to determine a longer 

term average emission limit that may be 

considered comparably stringent.3 The 

guidance also addresses a variety of 

related topics, such as 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 EPA’s Guideline on Air 

Quality Models (40 CFR part 51, 

appendix W).4 In 2005, EPA 

promulgated AERMOD as the Agency’s 

preferred near-field dispersion modeling 

for a wide range of regulatory 

applications addressing stationary 

sources (including 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 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. Estimated concentrations 

should include ambient background 

concentrations, follow the form of the 

standard, and 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’’ (EPA, 

2010). 

C. RACM/RACT 

To be approved by EPA, the SIP must 

provide for attainment of the standard 

based on SO2 emission reductions from 

control measures that are permanent 

and enforceable.5 At a minimum, states 

must consider all RACM and RACT 

measures that can be implemented in 

light of the attainment needs for the 

affected area(s), and include all 

necessary measures in order to attain 

the NAAQS.6 See ‘‘General Preamble for 

the Implementation of Title I of the 

Clean Air Act Amendments of 1990; 

Proposed Rule,’’ 57 FR 13498, 13547 

(Apr. 16, 1992) (‘‘General Preamble’’). 

D. New Source Review (NSR) 

Part D of title I of the CAA prescribes 

the procedures and conditions under 

which a new major stationary source or 

major modification may obtain a 

preconstruction permit in an area 

designated nonattainment for any 

criteria pollutant. The nonattainment 

NSR permitting requirements in section 

172(c)(5) and 173 of the CAA are among 

‘‘the requirements of this part’’ to be 

submitted to EPA as part of a revised 

SIP for a nonattainment area within 18 

months of the effective date of a 

designation or redesignation to 

nonattainment. Air agencies that already 

have a nonattainment NSR permitting 

program applicable to areas previously 

designated nonattainment on the basis 

of the previous SO2 NAAQS (annual, 

24-hour or 3-hour averaging periods) 

may be able to use that existing program 

to authorize the construction and 

modification of major stationary sources 

of SO2 that would locate in a new 2010 

SO2 nonattainment area.7 However, 

because of the limited number of 

nonattainment areas designated under 

the previous SO2 NAAQS, and since 

nonattainment NSR rules in some states 

may not automatically address areas 

designated nonattainment for newly 

promulgated air quality standards, some 

air agencies may not have 

nonattainment NSR rules that apply 

when new nonattainment areas for the 

1-hour primary SO2 standard are 

designated. In such cases, within 18 

months of designation, such agencies 

would need either to revise their 

existing nonattainment NSR programs 

or to develop new programs to enable 

the permitting of any major stationary 

source of SO2 locating in a 

nonattainment area under the 2010 SO2

NAAQS. 

E. RFP 

Section 171(1) of the CAA defines 

RFP as ‘‘such annual incremental 

reductions in emissions of the relevant 

air pollutant as are required by 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 EPA has 

previously explained, this definition is 

most appropriate for pollutants that are 

emitted by numerous and diverse 

sources, where the relationship between 

any individual source and the overall 

air quality is not explicitly quantified, 

and where the emission reductions 

necessary to attain the NAAQS are 

inventory-wide. General Preamble, at 

13547. EPA has also previously 


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explained that the definition is 

generally less pertinent to pollutants 

like SO2 that usually have a limited 

number of sources affecting areas of air 

quality that are relatively well defined, 

and emissions control measures for such 

sources result in swift and dramatic 

improvement in air quality. Id. For SO2,

there is usually a single ‘‘step’’ between 

pre-control nonattainment and postcontrol attainment. Therefore, for SO2, 

with its discernible relationship 

between emissions and air quality, and 

significant and immediate air quality 

improvements, RFP is best construed as 

‘‘adherence to an ambitious compliance 

schedule.’’ Id. This means that the state 

must ensure that affected sources 

implement appropriate control 

measures as expeditiously as practicable 

in order to ensure attainment of the 

standard by the applicable attainment 

date. 

F. Contingency Measures 

In accordance with section 172(c)(9) 

of the CAA, SO2 nonattainment plans 

must include contingency measures in 

order to obtain EPA approval. These 

measures must be fully adopted and 

should contain trigger mechanisms and 

an implementation schedule. In 

addition, they should be included in the 

SIP as measures that will take effect 

without further action by the state or 

EPA. Contingency measures are 

implemented if RFP targets are not 

achieved, or if the nonattainment area 

has not reached attainment by the 

applicable attainment date. Where an 

area has already achieved attainment by 

the attainment date, it has no need to 

rely on contingency measures to come 

into attainment or to make further 

progress to attainment. 

EPA has explained that planning for 

SO2 poses special considerations. SO2

control measures are based on what is 

directly and quantifiably necessary to 

attain the NAAQS, and it would be 

unlikely for an area to implement the 

necessary emissions control yet fail to 

attain the NAAQS. General Preamble at 

13547. Therefore, for SO2 nonattainment 

plans, EPA guidance also observes that 

the contingency measures requirement 

can be satisfied by the air agency having 

a comprehensive program to identify 

sources of violations of the SO2 NAAQS 

and to undertake an ‘aggressive’ followup for compliance and enforcement.’’ 

Id. The 2014 SO2 Guidance provides 

further explanation of the context in 

which such an approach may be 

appropriate for addressing section 

172(c)(9) contingency measure 

requirements for SO2. This approach for 

meeting contingency measure 

requirements does not preclude a state 

from requiring additional contingency 

measures that are enforceable and 

appropriate for a particular source or 

source category. General Preamble at 

13547. 

III. Modeled Attainment Plans 

The following discussion evaluates 

various features of the modeling and 

other elements of Illinois’ 

nonattainment plans for the Lemont and 

Pekin areas. 

A. Model Selection 

Illinois’ attainment demonstrations 

used AERMOD, the preferred model for 

these applications. Illinois used version 

14134 of this model, using regulatory 

default mode, with no beta options. This 

version of AERMOD was the 

recommended version at the time the 

state conducted its nonattainment 

planning, and in any case the results of 

this version are likely to be similar to 

those that more recent versions would 

provide, so EPA finds use of this version 

of AERMOD to be acceptable. 

Illinois performed an Auer’s land use 

analysis which indicates that the 

Lemont area is approximately 79 

percent rural, and the Pekin area is 

approximately 88 percent rural. A 

technical support document provides 

figures, taken from Illinois’ submittal, 

that show the land use in the Lemont 

and Pekin areas, respectively, 

illustrating the areas that are 

characterized as rural, not urban, in the 

Auer classification system. EPA finds it 

appropriate to model these areas as rural 

areas. 

B. Meteorological Data 

Illinois chose the Chicago O’Hare 

surface station (WBAN #94846) and the 

Davenport, Iowa upper air station 

(WBAN #94982) as the most 

representative meteorological stations 

for the Lemont area. Illinois chose the 

Peoria surface station (WBAN #14842) 

and Lincoln upper air station (WBAN 

#048233) as the most representative 

meteorological stations for the Pekin 

area. These are the closest National 

Weather Service surface stations to each 

respective area. The State determined 

these stations to be the most 

representative for the respective 

modeling domains. The upper air 

stations were chosen on the basis of 

regional representativeness. EPA finds 

Illinois’ choices of surface and upper air 

meteorological stations appropriate 

based on: (1) The suitability of 

meteorological data for the study area; 

and (2) the actual similarity of surface 

conditions and surroundings at the 

emissions source/receptor impact area 

compared to the locations of the 

meteorological instrumentation towers. 

C. Emissions Data 

Illinois chose to include emissions 

data from all permitted sources within 

each modeling domain, which consists 

of a 50 kilometer radius circumscribing 

an area centered on the violating 

monitor. Illinois chose not to evaluate 

which sources would ‘‘cause a 

significant concentration gradient’’ (40 

CFR part 51, appendix W), because that 

analysis would result in a greater 

modeling burden, along with significant 

subjectivity. The inclusion of all 

permitted sources assures that Illinois’ 

modeled concentrations are 

conservative, in that it adds impacts that 

may also be represented in the 

background concentration. 

Except for the Powerton Generating 

Station (Powerton) located in the Pekin 

area, the emission limits for newly 

limited sources, as outlined in Illinois’ 

attainment demonstration, correspond 

to the revised sulfur limitations on a 1- 

hour basis and are found in 35 Illinois 

Administrative Code Part 214. The 

applicable emission limit for Powerton 

is established on a 30-day average basis 

and is lower than the modeled 1-hour 

attainment emission rate (the critical 

emission value) by virtue of application 

of an adjustment factor determined and 

applied in accordance with the 2014 

SO2 Guidance. 

Specifically, as discussed further 

below, the 30-day average limit is about 

58 percent of the modeled 1-hour 

emission rate, or, conversely, the 

modeled emission rate (the critical 

emission value) is about 74 percent 

higher than the 30-day average limit. 

The emission limits for sources in the 

Lemont area are all on a 1-hour average 

basis and equal the modeled emissions 

rate. EPA finds Illinois’ choice of 

included sources and modeled 

emissions appropriate. 

D. Emission Limits 

An important prerequisite for 

approval of an attainment plan is that 

the emission limits that provide for 

attainment be fully enforceable. The 

revised limits for significant 

contributing sources are codified in 

Illinois’ sulfur limitations rule at 35 

Illinois Administrative Code Part 214, 

Subpart AA, titled ‘‘Requirements for 

Certain SO2 Sources.’’ The rules also 

include associated monitoring, testing, 

and recordkeeping and reporting 

requirements. A summary of the limits, 

showing the sum of the allowable 

hourly emissions for each plant, is 

shown in Table 1. As shown in this 

table, the emission limit for Powerton is 


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expressed as a 30-day average limit. 

Other limits in the rule are expressed as 

1-hour average limits. EPA’s review of 

Illinois’ nonattainment plan addresses 

the use of these limits, both with respect 

to the general suitability of using such 

limits in attainment demonstrations, 

and whether Illinois has demonstrated 

that the particular limits included in the 

plan provide for attainment. 

TABLE 1—EMISSION LIMITS IN SUBMITTED ILLINOIS RULES

Facility 

Sum of 

allowable 

emissions 

(pounds/hour) 

Averaging time 

for limits 

Limits for Sources in or near Lemont Area 

Ingredion ............................................................................................................................................................. 175.91 1-hour. 

Midwest Generation Joliet .................................................................................................................................. 855.26 1-hour. 

Midwest Generation Will County ........................................................................................................................ 5,145.14 1-hour. 

Owens Corning ................................................................................................................................................... 82.78 1-hour. 

Oxbow Midwest Calcining ................................................................................................................................... 187.00 1-hour. 

Limits for Sources in or near Lemont Area 

Aventine .............................................................................................................................................................. 26.80 1-hour. 

Illinois Power E.D. Edwards ............................................................................................................................... 4,856 1-hour. 

Midwest Generation Powerton ............................................................................................................................ 3,452 30-day. 

Illinois also modeled a number of 

other sources in its attainment 

demonstration, basing allowable 

emissions on limits established in state 

permits. EPA addresses the 

enforceability of the limits in the plans 

and Illinois’ use of a 30-day average 

emission limit for Powerton below. 

1. Enforceability 

In preparing its plans, Illinois adopted 

revisions to a previously approved state 

regulation governing emissions of SO2. 

These rule revisions were adopted by 

the Illinois Pollution Control Board 

following established, appropriate 

public review procedures. In addition, 

the rule revisions provide unambiguous, 

permanent emission limits, expressed in 

pounds per hour of allowable SO2

emissions, that, if exceeded by a source, 

would be clear grounds for an 

enforcement action. 

In comments to the state, Sierra Club 

requested that the rule being adopted by 

Illinois ‘‘incorporate enforceable 

restrictions for all sources for which 

emissions reductions were included in 

the modeling that demonstrated 

attainment.’’ EPA’s 2014 SO2 Guidance 

addresses the need for enforceability of 

the limits necessary to provide for 

attainment. The Guidance states, ‘‘An 

approvable attainment demonstration 

would . . . demonstrate that the 

emission limits in the plan will suffice 

to provide for timely attainment . . . In 

cases where the necessary emission 

limits have not previously been made a 

part of the SIP, or have not otherwise 

become federally enforceable, the plan 

needs to include the necessary 

enforceable limits in adopted form 

suitable for incorporation into the SIP.’’ 

See 2014 SO2 guidance, p. 9. 

The most significant sources in and 

near the designated nonattainment areas 

are subject to new emission limits that 

Illinois adopted as part of its part 214 

rules. In particular, all of the sources 

that needed to reduce emissions in 

order for the nonattainment areas to 

attain the standard or that needed a 

reduced allowable emission level in 

order for the areas to maintain 

attainment of the standard are subject to 

limits adopted as part of the rule. Thus, 

the sources that are most critical to the 

future success of the attainment plans 

(including all of the significant units at 

these sources) are subject to limitations 

adopted in Illinois’ rule. Illinois did not 

submit already federally enforceable 

permits for incorporation into the SIP, 

even if the modeling showing future 

attainment accounted for such limits. 

However, as previously discussed, all of 

the emission reductions that Illinois 

identified as necessary to bring the 

Lemont and Pekin areas into attainment 

are mandated by emission limits in the 

rule. Those sources for which Illinois’ 

modeled emissions were based on 

federally enforceable limits already 

established in permits rather than in the 

new rules are sources that are already 

required to meet emission levels that 

should, combined with the new rule 

limits, provide for attainment of the 

standard, so that no further emission 

reductions are necessary for these 

sources in order for the SIP to provide 

for NAAQS attainment. 

EPA reviewed the basis of the existing 

emission limits for the most significant 

of those sources not needing to reduce 

emissions below existing levels. In 

general, for these sources, the limits that 

underlie the allowable emission levels 

that Illinois modeled were established 

in federally enforceable construction 

permits. In some cases, these permits 

were to authorize major modifications 

or major new sources, in accordance 

with requirements for prevention of 

significant deterioration (PSD). In other 

cases, notably for the refineries, Illinois 

issued these limits in federally 

enforceable form in accordance with a 

federal-state consent decree. For 

example, the limits on emissions from 

the primary emission sources at CITGO, 

originally established by consent decree, 

have been incorporated into PSD permit 

number 05070003. The limits 

established in such permits are federally 

enforceable. In accordance with EPA’s 

guidance on the use of federally 

enforceable limits, EPA finds that these 

limits are an appropriate estimate of the 

maximum allowable emissions under 

the plans, and so EPA finds that these 

limits represent an appropriate basis for 

modeling to determine whether Illinois’ 

nonattainment plan provides for 

attainment. 

Illinois has requested EPA to approve 

revisions to emission limits for 

significant sources within the Pekin and 

Lemont areas in 35 Illinois 

Administrative Code part 214, as part of 

the SIP, and EPA proposes to approve 

these new emission limits because they, 

in combination with permit limits that 

are already federally enforceable, 

provide adequate enforceability of the 

necessary emission limits for the 

purposes of Illinois’ nonattainment 

plans. 


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8Since this 3-year period has 1,096 days, and the 

data set for each hour of the day is divided into four 

seasons of data sets, the data set for the 

determination of each of the 96-hour and seasonspecific background concentration includes a 

maximum of about 274 values. The selection of the 

second highest value is considered to provide an 

appropriate degree of conservatism in determining 

the background concentration for each hour and 

season. AERMOD then reports results that reflect 

the addition of the appropriate background value; 

for example, concentrations reported for an 8 a.m. 

hour in springtime reflect the sum of the source 

impacts for that hour plus the springtime 8 a.m. 

background concentration. 

2. Longer Term Average Limits 

As noted above, the 2014 SO2

Guidance discusses the option to 

establish limits with averaging times up 

to 30 days in length that are comparably 

stringent to the 1-hour average limit that 

would otherwise have been set, and 

recommends a detailed procedure for 

determining such a comparably 

stringent limit. The Guidance also notes 

that it might be appropriate to establish 

supplemental limits in order to limit the 

magnitude and/or frequency of elevated 

emissions, as a means of further 

reducing the likelihood of elevated 

emissions occurring on those occasions 

when the meteorology is conducive to 

high concentrations of SO2. 

Based on the variability of emissions 

at Powerton, Illinois opted to set the 

emission limit for this facility on a 30- 

day average basis. Illinois closely 

followed the recommendations of the 

2014 SO2 Guidance in determining an 

appropriate level for this limit. As a first 

step, Illinois conducted modeling which 

determined that the 1-hour emission 

limit that would provide for attainment 

(the critical emissions value) would be 

6,000 pounds of SO2 per hour. That is, 

Illinois conducted a series of modeling 

runs identifying baseline allowable air 

quality (in absence of emission 

reductions), evaluating the air quality 

consequences of feasible emission 

reductions, and ultimately identifying a 

set of reduced allowable emission levels 

that would provide for attainment. In 

this attaining set of ‘‘critical emission 

levels,’’ the ‘‘critical emission level’’ for 

Powerton was 6,000 pounds per hour. 

Illinois then used a database of hourly 

SO2 emissions data from a source 

comparable with Powerton to determine 

the historical and expected future 

relationship between 1-hour and 30-day 

average actual emission levels of a 

source using the control technology that 

Powerton will employ. Illinois’ 

submittal notes that Powerton 

(presumably for purposes of satisfying 

the Mercury and Air Toxics Standards) 

is expected to install ‘‘a trona injection 

dry FGD system for the control of SO2

emissions before 2017, so historical data 

from the units at the source would not 

be appropriate’’ as a basis for 

determining the prospective 

relationship between 1-hour and 30-day 

average emissions once the control is 

installed. See Illinois submittal, 

Technical Support Document, page 9. 

‘‘As a substitute, [Illinois used] a data 

set consisting of 42 months of emissions 

data from the Potomac River Generating 

Station, located in Alexandria, Virginia, 

[which] are similar to the Powerton 

units, and were operated with trona 

injection systems during the time this 

data set was created.’’ Id. Using this data 

set, Illinois determined the 99th 

percentile of the historical 1-hour values 

in this data set to be 1,107 pounds per 

hour and the 99th percentile of the 

historical 30-day average values 

calculated from this data set to be 637 

pounds per hour. Illinois used the ratio 

between these two 99th percentile 

values (i.e., approximately 58 percent) 

as an adjustment factor to multiply by 

the critical emissions value (the 

otherwise applicable 1-hour emission 

limit) of 6,000 pounds per hour to 

determine a comparably stringent 30- 

day average limit of 3,452 pounds per 

hour. This adjustment factor is quite 

similar to, and slightly more 

conservative (i.e., it reflects a more 

stringent long term limit) than, the 

average adjustment factor discussed in 

EPA’s 2014 SO2 Guidance for facilities 

using dry scrubbers, an average 

adjustment factor of 63 percent. See 

appendix D of EPA’s 2014 Guidance. 

As noted above, EPA’s 2014 SO2

Guidance notes the benefit of 

supplementing long term average limits 

with additional limits to reduce the 

likelihood and/or the magnitude of 

emission levels above the 1-hour critical 

emission value. For this purpose, 

Illinois’ rules supplement the 30-day 

average limit for Powerton with a 

requirement that emissions not exceed 

6,000 pounds per hour more than 5 

percent of the hours (as a 1-hour 

average) during any 30-day averaging 

period. By constraining the likelihood of 

elevated emissions, and thereby 

reducing the likelihood that elevated 

emissions will occur at times when 

meteorology is conducive to high SO2

concentrations, this supplemental limit 

further strengthens the degree of 

confidence that Illinois’ plan for the 

Pekin area should result in attainment. 

Based on a review of the state’s 

submittal, the 3,452 pounds per hour 

30-day average limit for Powerton, 

supplemented with a limit on the 

percentage of time that Powerton may 

exceed the 6,000 pounds per hour 

critical emission value, provides a 

suitable alternative to establishing a 

6,000 pounds per hour 1-hour average 

emission limit for this source. The state 

used a suitable database and then 

applied an appropriate adjustment, 

yielding an emission limit that has 

comparable stringency to the 1-hour 

average limit that the state determined 

would otherwise have been necessary to 

provide for attainment. While the 30- 

day average limit allows for occasions in 

which emissions are higher than the 

level that would be allowed under the 

1-hour limit, the state’s limit 

compensates by requiring average 

emissions to be lower than the level that 

would otherwise have been required by 

a 1-hour average limit. Further, the 

supplemental limit adopted by Illinois 

ensures that elevated emissions will be 

infrequent. Thus, the 30-day average 

limit of 3,452 pounds per hour as 

supplemented is comparably as 

stringent as a 1-hour limit of 6,000 

pounds per hour. Furthermore, Illinois’ 

modeling of 6,000 pounds per hour for 

Powerton is an appropriate means of 

assessing whether the 30-day average 

limit of 3,452 pounds per hour plus 

supplemental limit provides for 

attainment. 

Based on EPA’s review of this 

information, the 30-day average limit for 

Powerton, in combination with other 

limitations in the state’s plan (most 

notably the limits summarized in Table 

1 above), should provide for attainment. 

E. Background Concentrations 

Illinois used seasonally varying 

hourly background data. These values 

were taken from an SO2 monitor in 

Oglesby, Illinois, which is located 

approximately half way between the 

two areas. There were 24 hourly values 

for each season, for a total of 96 

monitored concentration values. Each of 

these values represents a three-year 

average (2011–2013) of the second 

highest hourly concentration for each 

season.8 The values that Illinois 

determined range from 1.54 to 12.22 

micrograms per cubic meter (mg/m3). 

EPA has reviewed these background 

concentrations and finds these values 

appropriate as modeling inputs. 

F. Review of Modeling Concerns 

Addressed by Illinois 

During preparation of its 

nonattainment plans, Illinois received 

and responded to a number of 

comments by, among others, the Sierra 

Club and the Environmental Law and 

Policy Center that EPA believes warrant 

further review and explanation. Sierra 

Club noted that the nonattainment plans 

provide only a relatively small margin 

of attainment, and Sierra Club 

commented (among other comments) 


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9For example, for CITGO, see Civil Action 

Number H–04–3883 entered January 26, 2005 in the 

Southern District of Texas. 

that in this context, various types of 

emissions that Illinois does not account 

for could result in these areas violating 

the standard. EPA has reviewed the 

comments that Sierra Club provided to 

Illinois and the response that Illinois 

provided in a document dated August 

28, 2015. (These comments and 

responses were included in Illinois’ SIP 

submittal and thus are available in the 

docket for this action). 

First, Sierra Club expressed concerns 

about emissions from modeled sources 

that are not subject to Illinois 

Administrative Code section 214.603. 

Section 214.603 includes the following 

sources: Aventine Renewable Energy; 

Illinois Power Holdings E.D. Edwards; 

Ingredion Bedford Park; Midwest 

Generation Joliet; Midwest Generation 

Powerton; Midwest Generation Will 

County; Owens Corning; and Oxbow 

Midwest Calcining. Sierra Club 

commented that emissions from startup, shutdown, and malfunction that 

represent noncompliance could lead to 

a violation of the NAAQS. Illinois 

responded that maximum allowable 

emissions for the sources were used, 

and that these allowable emissions are 

enforceable through emission 

limitations in other regulations or 

permit conditions. EPA agrees with 

Illinois’ response, finding that while 

emissions above allowable levels may 

occasionally occur, excess emissions 

that are prohibited by applicable 

requirements (whether they are 

occurring during start-up, shutdown, or 

malfunctions or at other times) need not 

be considered in evaluating whether a 

plan provides for attainment. That is, if 

a plan requires emissions to be 

sufficiently low to achieve attainment, 

EPA considers the plan to satisfy the 

requirement to provide for attainment, 

and the possibility of noncompliance 

that causes violations is an enforcement 

concern and not an indication that the 

plan has failed to provide for 

attainment. 

Second, Sierra Club expressed 

concern regarding emissions from minor 

sources. Sierra Club expressed 

particular concern about minor sources 

being authorized by ‘‘permits by rule’’ 

that exempt the sources from review of 

their impact on SO2 air quality. In 

expressing this concern, Sierra Club did 

not identify any permits by rule that had 

been issued or that were under 

consideration, or levels of emissions 

that might arise from such 

authorizations that may cause concern 

about maintaining attainment of the 

standard. Furthermore, Sierra Club did 

not identify examples of source types 

that might be minor enough to be 

authorized by a permit by rule and yet 

significant enough to cause the potential 

for violations of the SO2 standard. 

Illinois responded that no such ‘‘permits 

by rule’’ exist that exempt minor 

sources with SO2 emissions from review 

of air quality impacts. Illinois further 

noted that, even in the hypothetical 

situation that such a permit by rule 

existed, new minor sources, and minor 

modifications at major sources, in 

general contribute very little to SO2

ambient concentrations, but in any case 

that Illinois conducts additional 

modeling in cases where the potential 

for air quality problems exists. Illinois’ 

minor source permitting program 

provides adequate protection against 

minor sources and minor modifications 

causing violations of the SO2 standard. 

Third, Sierra Club contended that 

while Illinois claims more than 99 

percent emission reduction at many 

sources, presumably based on the 

requirement that Illinois has now 

adopted rules requiring industrial 

sources that burn diesel fuel or residual 

oil to burn ultra-low sulfur fuel, these 

requirements cannot achieve the 99 

percent reduction at modeled sources 

that Illinois claimed. It appears that 

Illinois is claiming that the rules 

reduced allowable emissions by more 

than 99 percent, while Sierra Club is 

asserting that there will be no such 

percent reduction in actual emissions. 

Illinois responded that the relevant 

issue is whether the emission level 

required by the rules is an appropriate 

level consistent with attaining the 

standard, not the percent reduction in 

relation to prior actual or allowable 

emissions. That is, the percent 

reduction that results from Illinois’ 

rules, and whether it is calculated on 

the basis of actual or allowable 

emissions, is not germane to the 

attainment demonstration, which is 

designed to demonstrate that allowable 

emissions are sufficiently low to 

provide for attainment. EPA agrees that, 

irrespective of the precise relationship 

between current and required future 

emissions, i.e., irrespective of what 

emission reduction percentage the rule 

requires relative to current emission 

levels, the rules require emissions to be 

at levels that provide for attainment. 

Fourth, Sierra Club expressed concern 

that the flares modeled by Illinois will 

have ‘‘much higher’’ emissions during 

routine operations, such as flaring off 

gases during start-up, shutdown, and 

malfunction events when compared to 

pilot emissions, and that Illinois did not 

model these higher emission rates. 

Illinois responded that the flares have 

limits on their allowable emissions 

(which apply at all times, including 

during the events of concern to the 

Sierra Club), and the flares were 

modeled at their maximum allowable 

emission rates. The most significant 

flares in the Lemont area are at the 

CITGO and Exxon-Mobil refineries; 

these flares were addressed in a consent 

decree,9 with terms and conditions 

subsequently incorporated into federally 

enforceable state permits requiring 

compliance with new source 

performance standards. The most 

significant flare in the Pekin area, at 

Aventine, is subject to emission limits 

in the state rules submitted in Illinois’ 

plan. As noted above, these emission 

limits are practically enforceable, and 

the approach taken by Illinois in 

modeling maximum allowable emission 

rates is consistent with EPA 

recommendations for attainment 

demonstration modeling. EPA agrees 

with Illinois’ rationale and conclusions 

regarding Sierra Club’s concerns about 

Illinois’ modeling analysis. 

Finally, Sierra Club expressed 

concern regarding the impacts of 

possible emission ‘‘spikes’’ at Powerton, 

i.e., occasions with elevated emissions 

that would be permissible under the 

3,452 pound per hour 30-day average 

emission limit applicable to the facility. 

Sierra Club in particular urged the 

adoption of supplemental limits to 

restrict the magnitude and frequency of 

these emission spikes. As described 

earlier, Illinois responded by adopting a 

supplemental limit requiring that no 

more than 5 percent of the hours in any 

30-day averaging period may have 

emissions in excess of 6,000 pounds per 

hour, which is the modeled critical 

emissions value. EPA believes this 

supplemental limit appropriately 

addresses Sierra Club’s concern. 

G. Summary of Results 

The final dispersion modeling results 

submitted by Illinois show design value 

concentrations of 190.9 and 196.2 mg/m3

for the Lemont and Pekin nonattainment 

areas, respectively. Both of these design 

value concentrations are below 75 ppb, 

which corresponds to 196.4 mg/m3, and 

therefore Illinois’ modeling analysis 

demonstrates attainment of the 2010 

SO2 NAAQS for the Lemont and Pekin 

areas. EPA has reviewed Illinois’ 

attainment demonstrations, agrees with 

Illinois’ submitted results, and proposes 

to determine that Illinois’ plans provide 

for attainment of the 2010 primary SO2

NAAQS in the Lemont and Pekin 

nonattainment areas. 


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IV. Review of Residual and Distillate 

Fuel Oil Sulfur Content Limits 

In conjunction with its adoption of 

SO2 emission limits for major sources, 

Illinois adopted rule revisions to limit 

the sulfur content of distillate and 

residual fuel oil combusted at stationary 

sources throughout the state. Consistent 

with trends toward increasing 

availability and use of lower sulfur oil 

of all kinds, these limits were intended 

to assure that the considerable number 

of generally smaller boilers that burn 

these fuels use fuels with relatively low 

sulfur content. The new limits adopted 

by Illinois will help protect air quality 

in the entire state, including the Lemont 

and Pekin nonattainment areas. As a 

result, EPA proposes to approve these 

rule amendments as part of the SIP. 

On and after January 1, 2017, the 

sulfur content of residual fuel oil 

combusted at stationary sources will be 

limited to 1,000 parts per million (ppm), 

and sulfur content of distillate fuel oil 

will be limited to 15 ppm. These limits 

apply to facilities that exclusively burn 

liquid fuel. These limits were adopted 

as part of Title 35 of Illinois 

Administrative Code part 215 subparts 

B and D, in sections 214.121, 214.122, 

and 214.161. Section 214.121(b) sets 

these limits for large sources (sources 

with actual heat input greater than 73.2 

megawatts (MW)), and section 

214.122(b) sets these limits for small 

sources (sources with actual heat input 

smaller than, or equal to, 73.2 MW). 

Section 214.161(c) and (d) set 

exceptions from the sulfur content 

limitations mentioned above for specific 

sources. Section 214.161(c) lists 

exceptions for Midwest Generation 

Joliet, Powerton, Waukegan, and Will 

County power stations or electric 

generating units (EGUs). These sources 

must comply with the following 

limitations: (1) From January 1, 2016 

through December 31, 2018, the sulfur 

content of all distillate fuel oil 

purchased for use by the listed EGUs 

must not exceed 15 ppm; (2) from 

January 1, 2017 through December 31, 

2018, the sulfur content of all distillate 

fuel oil used by the listed EGUs must 

not exceed 500 ppm; and (3) on and 

after January 1, 2019, the sulfur content 

of all distillate fuel oil used by the listed 

EGUs must not exceed 15 ppm. Section 

214.161(d) sets an exception for 

Caterpillar Montgomery, and sets the 

following limit: On and after January 1, 

2016, the sulfur content of all distillate 

fuel oil purchased for use by this source 

must not exceed 15 ppm, and the sulfur 

content of all distillate fuel oil used by 

this source must not exceed 500 ppm. 

These exemptions provide the listed 

sources with additional time to burn 

existing stocks of higher sulfur oils, but 

ultimately require these sources to meet 

the same sulfur content limits as apply 

to other sources in the state. 

For the sources to which these 

alternate provisions apply that are in or 

near the Lemont or Pekin areas, the 

attainment modeling reflects the 

emissions that are allowable as of 

January 1, 2017, without regard to the 

tighter limits that apply two years 

thereafter. Thus, Illinois’ modeling 

shows that these short term extensions 

of the deadline for complying with the 

generally applicable oil sulfur content 

limits do not prevent timely attainment. 

In addition, for the rest of the state, 

these limits strengthen the SIP and help 

improve air quality. For these reasons, 

EPA proposes to approve these rule 

amendments. 

In the rulemaking adopting the above 

elements of its Part 214 rules, Illinois 

also adopted revisions to Part 225 and 

217. However, Illinois’ Lemont and 

Pekin nonattainment plans are not 

contingent on any of the provisions of 

these parts of Illinois administrative 

code, and these rules were not 

submitted as a part of this SIP revision 

request. Thus, EPA is taking no action 

with respect to those revisions as part of 

this action. 

V. Review of Other Plan Requirements 

A. Emissions Inventory 

The emissions inventory and source 

emission rate data for an area serve as 

the foundation for air quality modeling 

and other analyses that enable states to: 

(1) Estimate the degree to which 

different sources within a 

nonattainment area contribute to 

violations within the affected area; and 

(2) assess the expected improvement in 

air quality within the nonattainment 

area due to the adoption and 

implementation of control measures. As 

noted above, the state must develop and 

submit to EPA a comprehensive, 

accurate and current inventory of actual 

emissions from all sources of SO2

emissions in each nonattainment area, 

as well as any sources located outside 

the nonattainment area which may 

affect attainment in the area. See CAA 

section 172(c)(3). 

Illinois provided a comprehensive, 

accurate, and current inventory of 

emissions of SO2 in and within 50 

kilometers of the Lemont and Pekin 

areas. By addressing sources to this 

distance from the nonattainment areas, 

Illinois has developed a thorough list of 

the sources with any potential to cause 

impacts that warrant including in the 

areas’ attainment modeling. Illinois’ 

initial submittal provided inventories of 

allowable emissions, and then Illinois 

supplemented this information on May 

4, 2017 with a submittal of inventories 

of actual emissions. 

As noted above, these inventories 

addressed sources within 50 kilometers 

of the Lemont and Pekin nonattainment 

areas. These inventories addressed 425 

sources in and near Lemont and 48 

sources in and near Pekin. Once Illinois 

compiled its inventory of current 

allowable emissions, Illinois conducted 

modeling to determine the degree to 

which the applicable emission 

limitations allowed violations of the 

SO2 air quality standard. Illinois then 

conducted a series of additional 

modeling runs to determine a set of 

emission limits that would provide for 

attainment. In accordance with EPA 

guidance, Illinois’ attainment 

demonstration is based on modeling 

using allowable emissions to 

demonstrate that its plans provide for 

attainment. This reflects Illinois’ intent 

to ensure that emissions are required to 

be sufficiently low as to achieve 

attainment, i.e., that allowable 

emissions will not cause violations. 

Similarly, Illinois’ plans are designed to 

meet the other part D requirements on 

the basis of allowable emissions, for 

example by setting allowable emissions 

at a level that satisfy applicable 

requirements for RACT/RACM and RFP. 

Illinois did not use actual emissions in 

this planning process. Accordingly, 

Illinois initially provided an inventory 

of allowable emissions, which served 

the needs of the pertinent 

nonattainment planning requirements. 

Then, in its May 4, 2017, submittal, 

Illinois also submitted a comprehensive, 

accurate, current inventory of actual 

emissions. Tables 1 and 2 summarize 

actual emissions in 2014 for a subset of 

these sources, namely those sources that 

have actual SO2 emissions of at least 

100 tons per year. Therefore, Illinois has 

met the emission inventory requirement 

of CAA section 172(c)(3) for the Pekin 

and Lemont areas. 


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TABLE 2—ACTUAL 2014 SO2 EMISSIONS IN LEMONT AREA EXCEEDING 100 TONS PER YEAR

Source name Actual SO2

(tpy) 

Midwest Generations—Joliet Station 29 ............................................................................................................................................. 12,800 

Will County Generating Station ........................................................................................................................................................... 10,478 

Ingredion Incorporated Argo Plant ...................................................................................................................................................... 1,671 

Exxon Mobil Oil Corp ........................................................................................................................................................................... 1,562 

Koppers Inc .......................................................................................................................................................................................... 867 

CITGO Petroleum Corp ....................................................................................................................................................................... 346 

Ardagh Glass Inc ................................................................................................................................................................................. 145 

TABLE 3—ACTUAL 2014 SO2 EMISSIONS IN PEKIN AREA EXCEEDING 100 TONS PER YEAR

Source name Actual SO2

(tpy) 

Midwest Generation LLC ..................................................................................................................................................................... 16,717 

Illinois Power Resources Generating LLC—Edwards Energy Ctr ...................................................................................................... 8,278 

Aventine Renewable Energy, Inc ........................................................................................................................................................ 7,292 

Illinois Power Resources Generating LLC—Duck Creek Energy ....................................................................................................... 240 

Keystone Steel & Wire Co ................................................................................................................................................................... 129 

B. RACM/RACT 

Illinois’s plan reflects a number of 

strategies to reduce emissions at various 

facilities. In the Lemont area, the Joliet 

power plant and Unit 3 of the Will 

County power plant will cease burning 

coal and will instead either burn natural 

gas or ultra-low sulfur diesel. In the 

Pekin area, substantial emission 

reductions will result from conversion 

of the Aventine facility switching from 

burning coal to burning natural gas and 

from implementation of emission 

control equipment at the E.D. Edwards 

and Powerton power plants. Both areas 

will also benefit from statewide 

requirements for boilers burning fuel oil 

to burn low sulfur fuel. 

In its August 8, 2016, supplemental 

submittal, Illinois explained its 

rationale for concluding that the plans 

meet the RACM/RACT requirement in 

accordance with EPA guidance. 

Specifically, following EPA’s 

interpretation that RACT and RACM 

reflect ‘‘the level of emissions control 

that is necessary to provide for 

expeditious attainment of the NAAQS 

within a nonattainment area,’’ Illinois 

noted that its nonattainment plans 

require permanent and enforceable 

control measures that provide for timely 

attainment. 35 Illinois Administrative 

Code section 214.603 lists the 

appropriate source-specific SO2

emission limits by unit, in pounds per 

hour. Therefore, Illinois has satisfied the 

RACM/RACT requirements for the 

Lemont and Pekin areas. 

C. NSR 

EPA approved Illinois’ nonattainment 

new source review rules on December 

17, 1992 (57 FR 59928); September 27, 

1995 (60 FR 49780) and May 13, 2003 

(68 FR 25504). These rules provide for 

appropriate new source review for SO2

sources undergoing construction or 

major modification in the Lemont and 

Pekin areas without need for 

modification of the approved rules. 

Although these rules predated 

promulgation of the 2010 SO2 standards, 

these rules are written in a manner such 

that new sources within areas that 

become designated nonattainment for 

this new standard, such as the Lemont 

and Pekin areas, become subject to these 

nonattainment new source review 

requirements. Therefore, this 

requirement has been met for these 

areas. 

D. RFP 

In its August 8, 2016, supplemental 

submittal, Illinois explained its 

rationale for concluding that the plans 

met the requirement for RFP in 

accordance with EPA guidance. 

Specifically, Illinois’s rationale is based 

on EPA guidance interpreting the RFP 

requirement being satisfied for SO2 if 

the plan requires ‘‘adherence to an 

ambitious compliance schedule’’ that 

‘‘implement[s] appropriate control 

measures as expeditiously as 

practicable.’’ Illinois noted that its 

nonattainment plans provide for 

attainment as expeditiously as 

practicable, i.e., by January 1, 2017, and 

finds that the plans thereby satisfy the 

requirement for RFP. Therefore, Illinois 

has satisfied the RFP requirements for 

the Lemont and Pekin areas. 

E. Contingency Measures 

In its August 8, 2016, supplemental 

submittal, Illinois explained its 

rationale for concluding that the plans 

met the requirement for contingency 

measures in accordance with EPA 

guidance. Specifically, Illinois relies on 

EPA’s guidance, noting the special 

circumstances that apply to SO2 (as 

discussed above), and explaining on 

that basis why the contingency 

requirement in CAA section 172(c)(9) is 

met for SO2 by having a comprehensive 

program to identify sources of violations 

of the SO2 NAAQS and to undertake an 

aggressive follow-up for compliance and 

enforcement of applicable emissions 

limitations. Illinois stated that it has 

such an enforcement program pursuant 

to Section 31 of the Illinois 

Environmental Protection Act, 

identifying violators and taking prompt, 

appropriate enforcement action, and 

concludes that Illinois’ nonattainment 

plans satisfy contingency measure 

requirements. Therefore, Illinois has 

satisfied the contingency measure 

requirements for the Lemont and Pekin 

areas. 

VI. EPA’s Proposed Action 

EPA is proposing to approve Illinois’ 

submission as a SIP revision, which the 

state submitted to EPA on March 2, 

2016, and supplemented on August 8, 

2016, and May 4, 2017, for attaining the 

2010 1-hour SO2 NAAQS for the Lemont 

and Pekin SO2 nonattainment areas. 

These SO2 nonattainment plans 

include Illinois’ attainment 

demonstration for the Lemont and Pekin 

SO2 nonattainment areas. These 

nonattainment plans also address 

requirements for emission inventories, 

RACT/RACM, RFP, and contingency 

measures. Illinois has previously 

addressed requirements regarding 

nonattainment area new source review. 

EPA has determined that Illinois’ SO2


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46444 Federal Register / Vol. 82, No. 192 / Thursday, October 5, 2017 / Proposed Rules 

nonattainment plans meet the 

applicable requirements of CAA 

sections 172, 191, and 192. EPA is 

taking public comments for thirty days 

following the publication of this 

proposed action in the Federal Register. 

EPA will take all comments into 

consideration in our final action. 

VII. Incorporation by Reference 

In this rule, 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 incorporate by reference 

Illinois Administrative Code, Title 35, 

Subtitle B, Chapter I, Subchapter c, Part 

214, Sections 214.121, 214.122, 214.161, 

214.600, 214.601, 214.602, 214.603, 

214.604, and 214.605, effective 

December 7, 2015. EPA has made, and 

will continue to make, these documents 

generally available through 

www.regulations.gov, and/or at the EPA 

Region 5 Office (please contact the 

person identified in the FOR FURTHER

INFORMATION CONTACT section of this 

preamble for more information). 

VIII. Statutory and Executive Order 

Reviews 

Under the CAA, the Administrator is 

required to approve a SIP submission 

that complies with the provisions of the 

CAA and applicable Federal regulations. 

42 U.S.C. 7410(k); 40 CFR 52.02(a). 

Thus, in reviewing SIP submissions, 

EPA’s role is to approve state choices, 

provided that they meet the criteria of 

the CAA. Accordingly, this proposed 

action merely approves state law as 

meeting Federal requirements and does 

not impose additional requirements 

beyond those imposed by state law. For 

that reason, this proposed action: 

• Is not a significant regulatory action 

subject to review by the Office of 

Management and Budget under 

Executive Orders 12866 (58 FR 51735, 

October 4, 1993) and 13563 (76 FR 3821, 

January 21, 2011); 

• Does not impose an information 

collection burden under the provisions 

of the Paperwork Reduction Act (44 

U.S.C. 3501 et seq.); 

• Is certified as not having a 

significant economic impact on a 

substantial number of small entities 

under the Regulatory Flexibility Act (5 

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

• Does not contain any unfunded 

mandate or significantly or uniquely 

affect small governments, as described 

in the Unfunded Mandates Reform Act 

of 1995 (Pub. L. 104–4); 

• Does not have Federalism 

implications as specified in Executive 

Order 13132 (64 FR 43255, August 10, 

1999); 

• Is not an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

13045 (62 FR 19885, April 23, 1997); 

• Is not a significant regulatory action 

subject to Executive Order 13211 (66 FR 

28355, May 22, 2001); 

• Is not subject to requirements of 

section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (15 U.S.C. 272 note) because 

application of those requirements would 

be inconsistent with the Clean Air Act; 

and 

• 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 

(59 FR 7629, February 16, 1994). 

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 rule 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). 

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: September 17, 2017. 

Robert A. Kaplan, 

Acting Regional Administrator, Region 5. 

[FR Doc. 2017–21371 Filed 10–4–17; 8:45 am] 

BILLING CODE 6560–50–P 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R09–OAR–2017–0377; FRL–9968–89– 

Region 9] 

Approval of Arizona Air Plan Revision; 

San Manuel, Arizona; Second 10-Year 

Sulfur Dioxide Maintenance Plan 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to approve 

the second 10-year maintenance plan for 

the San Manuel area in Arizona for the 

1971 National Ambient Air Quality 

Standards (NAAQS or ‘‘standards’’) for 

sulfur dioxide (SO2). 

DATES: Any comments on this proposal 

must arrive by November 6, 2017. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R09– 

OAR–2017–0377 at https://

www.regulations.gov, or via email to 

Ashley Graham, Air Planning Office at 

graham.ashleyr@epa.gov. For comments 

submitted at Regulations.gov, follow the 

online instructions for submitting 

comments. Once submitted, comments 

cannot be removed or edited from 

Regulations.gov. For either manner of 

submission, the 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 (e.g., audio or video) 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. The 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. 

Docket: The index to the docket for 

this action is available electronically on 

the www.regulations.gov Web site and 

in hard copy at EPA Region IX, 75 

Hawthorne Street, San Francisco, 

California 94105. While all documents 

in the docket are listed in the index, 

some information may be publicly 

available only at the hard copy location 

(e.g., copyrighted material), and some 

may not be publicly available at either 

location (e.g., CBI). To inspect the hard 

copy materials, please schedule an 

appointment during normal business 

hours with the contact listed in the FOR

FURTHER INFORMATION CONTACT section 

below. 

FOR FURTHER INFORMATION CONTACT: 

Ashley Graham, EPA Region IX, (415) 

972–3877, graham.ashleyr@epa.gov. 

SUPPLEMENTARY INFORMATION: 

Throughout this document, the words 

‘‘we,’’ ‘‘us,’’ or ‘‘our’’ mean the EPA. 

Table of Contents 

I. Summary of Action 

II. Background 


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