Air Plan Approval; Illinois; Nonattainment Plans for the Lemont and Pekin SO2, 46434-46444 [2017-21371]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 82, Number 192 (Thursday, October 5, 2017)]
[Proposed Rules]
[Pages 46434-46444]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2017-21371]



[[Page 46434]]

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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.

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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 https://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 https://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.
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    \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.
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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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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.
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    \2\ An ``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.
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    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 
well-designed 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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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.
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    \3\ For 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.
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    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.
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    \4\ EPA published revisions to the Guideline on Air Quality 
Models on January 17, 2017.
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    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'').
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    \5\ See section 110(a)(2)(A) of the CAA.
    \6\ Section 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.''
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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.
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    \7\ The 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).
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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

[[Page 46438]]

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 post-
control 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' follow-up 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

[[Page 46439]]

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
------------------------------------------------------------------------
                                     Sum of
                                    allowable       Averaging time for
            Facility                emissions             limits
                                  (pounds/hour)
------------------------------------------------------------------------
                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.

[[Page 46440]]

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 ([mu]g/m\3\). EPA has reviewed these 
background concentrations and finds these values appropriate as 
modeling inputs.
---------------------------------------------------------------------------

    \8\ Since 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 
season-specific 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.
---------------------------------------------------------------------------

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)

[[Page 46441]]

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 start-up, 
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.
---------------------------------------------------------------------------

    \9\ For example, for CITGO, see Civil Action Number H-04-3883 
entered January 26, 2005 in the Southern District of Texas.
---------------------------------------------------------------------------

    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 [mu]g/m\3\ for the 
Lemont and Pekin nonattainment areas, respectively. Both of these 
design value concentrations are below 75 ppb, which corresponds to 
196.4 [mu]g/m\3\, 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.

[[Page 46442]]

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 t