[Federal Register Volume 83, Number 218 (Friday, November 9, 2018)]
[Proposed Rules]
[Pages 56002-56015]
[FR Doc No: 2018-24582]

-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R04-OAR-2017-0625; FRL-9986-36-Region 4]

Air Plan Approval; Kentucky; Attainment Plan for Jefferson County
SO2 Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve the State Implementation Plan (SIP) revision, submitted under a
cover letter dated June 23, 2017, by the Commonwealth of Kentucky,
through the Kentucky Division for Air Quality (KDAQ) on behalf of the
Louisville Metro Air Pollution Control District (District or Jefferson
County) to EPA, for attaining the 1-hour sulfur dioxide
(SO2) primary national ambient air quality standard (NAAQS)
for the Jefferson County SO2 nonattainment area (hereafter
referred to as the ``Jefferson County nonattainment area,''
``nonattainment Area'' or ``Area''). The Jefferson County nonattainment
area is comprised of a portion of Jefferson County in Kentucky
surrounding the Louisville Gas and Electric Mill Creek Electric
Generating Station (hereafter referred to as ``Mill Creek'' or
``LG&E''). This plan (hereafter called a ``nonattainment plan'' or
``SIP'' or ``attainment SIP'') includes Kentucky's attainment
demonstration and other elements required under the Clean Air Act (CAA
or Act). In addition to an attainment demonstration, the plan addresses
the requirement for meeting reasonable further progress (RFP) toward
attainment of the NAAQS, reasonably available control measures and
reasonably available control technology (RACM/RACT), base-year and
projection-year emissions inventories, enforceable emission limits,
nonattainment new source review (NNSR) and contingency measures. EPA
proposes to conclude that Kentucky has appropriately demonstrated that
the nonattainment plan provisions provide for attainment of the 2010 1-
hour primary SO2 NAAQS in the Jefferson County nonattainment
area by the applicable attainment date and that the nonattainment plan
meets the other applicable requirements under CAA.

DATES: Comments must be received on or before December 10, 2018.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R04-
OAR-2017-0625 at http://www.regulations.gov. Follow the online
instructions for submitting comments. Once submitted, comments cannot
be edited or removed from Regulations.gov. 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, 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: Richard Wong, Air Regulatory
Management Section, Air Planning and Implementation Branch, Air,
Pesticides and Toxics Management Division, U.S. Environmental
Protection Agency, Region 4, 61 Forsyth Street SW, Atlanta, Georgia
30303-8960. Mr. Wong can be reached via telephone at<PHONE_NUMBER> or
via electronic mail at [email protected].

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Requirement for Kentucky to Submit an SO2 Attainment
Plan for the Jefferson County Area
II. Requirements for SO2 Attainment Plans
III. Attainment Demonstration and Longer Term Averaging
IV. Review of Attainment Plan Requirements
    A. Emission Inventory
    B. Attainment Modeling Demonstration
    1. Model Selection
    2. Meteorological Data
    3. Emissions Data
    4. Emission Limits
    i. Enforceability
    ii. Longer Term Average Limits
    5. Background Concentration
    6. Summary of Modeling Results
    C. RACM/RACT
    D. New Source Review (NSR)
    E. Reasonable Further Progress (RFP)

    F. Contingency Measures
V. Incorporation by Reference
VI. EPA's Proposed Action
VII. Statutory and Executive Orders

I. Requirements for Kentucky to Submit an SO2 Plan for the Jefferson
County Area.

    On June 22, 2010 (75 FR 35520), 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 daily maximum 1-hour average
concentrations does not exceed 75 ppb, as determined in accordance with
Appendix T of 40 CFR part 50. See 40 CFR 50.17(a)-(b). On August 5,
2013 (78 FR 47191), EPA designated a first set of 29 areas of the
country as nonattainment for the 2010 SO2 NAAQS. See 40 CFR
part 81, subpart C. These designations included the Jefferson County
nonattainment area, which encompasses the primary SO2
emitting source Mill Creek and the nearby Watson Lane SO2
monitor (Air Quality Site (AQS) ID: 21-11-0051). These area
designations were effective October 4, 2013. Section 191 of the CAA
directs states to submit SIPs for areas designated as nonattainment 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.
Under CAA section 192(a), these SIPs are required to demonstrate that
their respective areas will attain the NAAQS as expeditiously as
practicable, but no later than 5 years from the effective date of
designation, which is October 4, 2018.
    For the Jefferson County nonattainment area (and many other areas),
EPA published a notice on March 18, 2016 (81 FR 14736), that Kentucky
(and other pertinent states) had failed to submit the required
SO2 nonattainment plan by the submittal deadline. This
finding initiated a deadline under CAA section 179(a) for the potential
imposition of NSR offset and highway funding sanctions. However,
pursuant to Kentucky's submittal of June 23, 2017,\1\ and EPA's
subsequent letter dated October 10, 2017, to Kentucky finding the
submittal to be complete and noting the termination of these sanctions
deadlines, these sanctions under section 179(a) were not and will not
be imposed as a result of Kentucky having missed the April 4, 2015,
submittal deadline. Under CAA section 110(c), EPA's March 18, 2016,
finding also triggered a requirement that EPA promulgate a federal
implementation plan (FIP) within two years of the finding unless, by
that time (a) the state has made the necessary complete submittal and
(b) EPA has approved the submittal as meeting applicable requirements.
EPA's FIP duty will be terminated if EPA issues a final approval of
Kentucky's SIP revision.
---------------------------------------------------------------------------

    \1\ EPA received Kentucky's submittal on July 6, 2017.
---------------------------------------------------------------------------

II. Requirements for SO2 Nonattainment Area Plans

    Nonattainment areas must provide SIPs meeting the applicable
requirements of the CAA, and specifically CAA sections 110(a), 172, 191
and 192 for the SO2 NAAQS. EPA's regulations governing
nonattainment SIPs are set forth at 40 CFR part 51, with specific
procedural requirements and control strategy requirements residing at
subparts F and G, respectively. Soon after Congress enacted the 1990
Amendments to the CAA, EPA issued general guidance on SIPs, in a
document entitled the ``General Preamble for the Implementation of
Title I of the Clean Air Act Amendments of 1990,'' published at 57 FR
13498 (April 16, 1992) (General Preamble). Among other things, the
General Preamble addressed SO2 SIPs and fundamental
principles for SIP control strategies. Id., at 13545-49, 13567-68. On
April 23, 2014, EPA issued guidance for meeting the statutory
requirements in SO2 SIPs under the 2010 primary NAAQS, in a
document entitled, ``Guidance for 1-Hour SO2 Nonattainment
Area SIP Submissions,'' available at https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf (hereafter referred to as
SO2 nonattainment guidance). In this guidance, EPA described
the statutory requirements for SO2 SIPs for nonattainment
areas, which include: 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); NNSR; enforceable emissions limitations and
control measures; and adequate contingency measures for the affected
area.
    For EPA to fully approve a SIP as meeting the requirements of CAA
sections 110, 172 and 191-192, and EPA's regulations at 40 CFR part 51,
the SIP for the affected area needs to demonstrate to EPA's
satisfaction that each of the aforementioned requirements have been
met. Under CAA sections 110(l) and 193, EPA may not approve a SIP that
would interfere with any applicable requirement concerning NAAQS
attainment and RFP, or any other applicable requirement, and no
requirement in effect (or required to be adopted by an order,
settlement, agreement, or plan in effect before November 15, 1990) in
any area which is a nonattainment area for any air pollutant, may be
modified in any manner unless it insures equivalent or greater emission
reductions of such air pollutant. EPA is proposing to approve
Kentucky's June 23, 2017, SO2 attainment SIP for the
Jefferson County nonattainment area because EPA has preliminarily
determined that the plan satisfies the aforementioned CAA and
regulatory requirements for nonattainment areas. Furthermore, EPA notes
that current 2015-2017 quality-assured and certified data for the
Watson Lane monitor (AQS ID: AQS ID: 21-11-0051) in the nonattainment
area indicates a design value below the 1-hour SO2 standard.

III. Attainment Demonstration and Longer Term Averaging

    CAA sections 172(c)(1) and (6) direct 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, and EPA has long
required that all SIPs and control strategies reflect four fundamental
principles of quantification, enforceability, replicability, and
accountability. General Preamble, at 13567-68. SO2
attainment plans must consist of two components: (1) Emission limits
and other control measures that assure implementation of permanent,
enforceable and necessary emission controls, and (2) a modeling
analysis which 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 primary SO2 NAAQS as
expeditiously as practicable, but by no later than the CAA maximum
attainment date for the affected area. In all cases, the emission
limits and control measures must be accompanied by appropriate methods
and conditions to determine compliance with the respective emission
limits and control measures and must be quantifiable (i.e., a specific
amount of emission reduction can be ascribed to the measures), fully-
enforceable (specifying clear, unambiguous and measurable requirements
for which compliance can be practicably determined), replicable (the
procedures for determining compliance are sufficiently specific and
non-subjective so that two independent entities applying the procedures
would obtain the same result), and accountable

(source specific limits must be permanent and must reflect the
assumptions used in the SIP demonstrations).
    EPA's April 2014 SO2 nonattainment guidance recommends
that the emission limits be expressed as short-term average limits
(e.g., addressing emissions averaged over one or three hours), but also
describes the option to establish emission limits with longer averaging
times of up to 30 days so long as the limits meet certain recommended
criteria. See SO2 nonattainment guidance, pp. 22 to 39. The
guidance recommends that--should states and sources utilize longer
averaging times--the longer term average limit should be a lower-
adjusted level that reflects a stringency comparable to the 1-hour
average limit at the critical emission value (CEV) shown by modeling to
provide for attainment that the plan otherwise would have set.
    EPA's SO2 nonattainment guidance provides an extensive
discussion of EPA's rationale for concluding that appropriately set
comparably stringent limitations based on averaging times as long as 30
days can be found to provide for attainment of the 2010 SO2
NAAQS. In evaluating this option, EPA considered the nature of the
standard, conducted detailed analyses of the impact concerning the 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. See also id.
at Appendices B, C, and D.
    As specified in 40 CFR 50.17(b), the 1-hour primary SO2
NAAQS is met at an ambient air quality monitoring site when the 3-year
average of the annual 99th percentile of daily maximum 1-hour average
concentrations is less than or equal to 75 ppb. In a year with 365 days
of valid monitoring data, the 99th percentile would be the fourth
highest daily maximum 1-hour value. The 2010 SO2 NAAQS,
including this form of determining compliance with the standard, was
upheld by the U.S. Court of Appeals for the District of Columbia
Circuit in Nat'l Envt'l Dev. Ass'n's Clean Air Project v. EPA, 686 F.3d
803 (D.C. Cir. 2012). Because the standard has this form, a single
hourly exceedance of the 75-ppb level does not create a violation of
the standard. Instead, at issue is whether a source operating in
compliance with a properly set longer term average could cause
exceedances, and if so the resulting frequency and magnitude of such
exceedances, and in particular, whether EPA can have reasonable
confidence that a properly set longer term average limit will provide
that the 3-year average of the annual fourth highest daily maximum 1-
hour value will be at or below 75 ppb. A synopsis of how EPA judges
whether such plans ``provide for attainment,'' based on modeling of
projected allowable emissions and in light of the SO2 NAAQS
form for determining attainment at monitoring sites, follows.
    For SO2 plans that are 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., in an ``average year'' \2\ shows three, not four days
with maximum hourly levels exceeding 75 ppb) is labeled the ``critical
emission value.'' The modeling process for identifying this 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.
---------------------------------------------------------------------------

    \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 hourly values (e.g., the
fourth highest maximum daily hourly concentration in a year with 365
days with valid data), this discussion and an example below uses a
single ``average year'' to simplify the illustration of relevant
principles.
---------------------------------------------------------------------------

    EPA recognizes that some sources have highly variable emissions,
for example due to variations in fuel sulfur content and operating
rate, that can make it extremely difficult, even with a well-designed
control strategy, to ensure in practice that emissions for any given
hour do not exceed the critical emission value. EPA also acknowledges
the concern that longer term emission limits can allow short periods
with emissions above the ``critical emission value,'' which, if
coincident with meteorological conditions conducive to high
SO2 concentrations, could in turn create the possibility of
a NAAQS exceedance occurring on a day when an exceedance would not have
occurred if emissions were continuously controlled at the level
corresponding to the critical emission value. However, for several
reasons, EPA believes that the approach recommended in its guidance
document suitably addresses this concern. First, from a practical
perspective, EPA expects the actual emission profile of a source
subject to an appropriately set longer term average limit to be similar
to the emission profile of a source subject to an analogous 1-hour
average limit. EPA expects this similarity because it has recommended
that the longer term average limit be set at a level that is comparably
stringent to the otherwise applicable 1-hour limit (reflecting a
downward adjustment from the 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.
    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, 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 to occasionally 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 that always emits 1000 pounds of SO2 per hour, which
results in air quality at the level of the NAAQS (i.e., results in a
design value of 75 ppb). Suppose further that in an ``average year,''
these emissions cause the 5-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

(lb/hr). It is theoretically possible for a source meeting this limit
to have emissions that occasionally exceed 1000 lb/hr, but with a
typical emissions profile, emissions would much more commonly be
between 600 and 800 lb/hr. 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 at the relevant times
on these 5 days are 800 lb/hr, 1100 lb/hr, 500 lb/hr, 900 lb/hr, and
1200 lb/hr, respectively. (This is a conservative example because the
average of these emissions, 900 lb/hr, 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 day would not have an exceedance
that otherwise would have occurred, and the fourth day would have a
concentration below, rather than at, 75 ppb. 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
SO2 nonattainment 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 its nonattainment
guidance, EPA expects that an emission profile with maximum allowable
emissions under an appropriately set comparably stringent 30-day
average limit is likely to have the net effect of having a lower number
of exceedances and better air quality than an emission profile with
maximum allowable emissions under a 1-hour emission limit at the
critical emission value. This result provides a compelling policy
rationale for allowing the use of a longer averaging period, in
appropriate circumstances where the facts indicate this result can be
expected to occur.
    The question then becomes 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 requirements in sections 110(a)(1) and 172(c)(1) and (6) for
SIPs to contain enforceable emissions limitations and other control
measures 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 judge 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 in this case the
desirability of accommodating real world emissions variability without
significant risk of violations, are also appropriate factors for EPA to
weigh in judging whether a plan provides a reasonable degree of
confidence that the plan will lead to attainment. Based on these
considerations, especially given the high likelihood that a
continuously enforceable limit averaged over as long as 30 days,
determined in accordance with EPA's nonattainment guidance, will 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 SO2 nonattainment guidance offers specific
recommendations for determining an appropriate longer term average
limit. The recommended method starts with determination of the 1-hour
emission limit that would provide for attainment (i.e., the 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 degree of stringency comparable to the otherwise
necessary 1-hour emission limit. This method uses a database of
continuous emission data reflecting the type of control that the source
will be using to comply with the SIP emission limits, which (if
compliance requires new controls) may require use of an emission
database from another source. The recommended method involves using
these data to compute a complete set of emission averages, computed
according to the averaging time and averaging procedures of the
prospective emission limitation. 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.
---------------------------------------------------------------------------

    \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 lb/hr.
---------------------------------------------------------------------------

    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), also referred to as Guideline. In 2005, EPA
promulgated AERMOD as the Agency's preferred near-field dispersion
modeling for a wide range of regulatory applications addressing
stationary sources (for example in estimating SO2
concentrations) in all types of terrain based on extensive
developmental and performance evaluation. Supplemental guidance on
modeling for purposes of demonstrating attainment of the SO2
NAAQS is provided in Appendix A to the SO2 nonattainment
guidance document referenced above. 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 of
stationary sources as applied consistent with EPA's Guideline is
technically appropriate, efficient and effective in demonstrating
attainment in nonattainment areas because it appropriately takes into
consideration combinations of meteorological and emission source
operating conditions that may contribute to peak ground-level
concentrations of SO2. The SIP modeling should follow
requirements in the Guideline for conducting a cumulative impact
assessment and, thus, should use EPA's preferred dispersion model, the
AERMOD modeling system (or approved alternative model) and follow
Section 8 of the Guideline in terms of characterizing contributions to
total concentrations.

IV. Review of Attainment 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) and
(4) and EPA's SO2 nonattainment guidance.
    The base year inventory establishes a baseline that is used to
evaluate emission reductions achieved by the control strategy and to
assess reasonable further progress requirements. Kentucky used 2011 as
the base year for emission inventory preparation. At the time of
preparation of the attainment SIP, 2011 reflected the most recent
triennial National Emission Inventory (NEI v2),\4\ Version 2 supported
the requirement for timeliness of data, and was also representative of
a year with violations of the primary SO2 NAAQS (i.e., one
of the 3-years for which EPA designated the area nonattainment).
---------------------------------------------------------------------------

    \4\ 2011 NEI Data--https://www.epa.gov/air-emissions-inventories/2011-national-emissions-inventory-nei-data (accessed
January 31, 2017).
---------------------------------------------------------------------------

    For the base-year inventory, Kentucky reviewed and compiled county-
level actual SO2 emissions for all source categories (i.e.,
point, mobile (on-road and non-road), area (non-point) and event
(wildfires and prescribed burns)) in Jefferson County and then utilized
county and partial county (the portion in the nonattainment area)
population and land use data to determine estimated SO2
emission inventories for sources of SO2 in the partial
county nonattainment area. The emissions inventory provided in the June
23, 2017, submission reflects the most current emissions profile for
all source categories. Additionally, EPA has provided supplemental
emissions information to accurately account for point source emissions
for the County. In Jefferson County, point sources account for
approximately 99 percent of the total county-level SO2
emissions. Kentucky provided an SO2 emission inventory for
those point sources in the County that emitted over 10 tons per year
(tpy) based on the 2011 NEI. Table 1 below shows county-level
SO2 emissions that emitted greater than 10 tpy in 2011.

   Table 1--Jefferson County 2011 Base Year Point Source SO2 Emission
                                Inventory
                                  (tpy)
------------------------------------------------------------------------
                                                           SO2 Emissions
                Plant/facility site name                       (tpy)

------------------------------------------------------------------------
Louisville Gas & Electric--Mill Creek...................       29,944.72
Louisville Gas & Electric--Cane Run.....................        7,823.72
Louisville Medical Center Steam Plant...................          475.90
Brown-Forman/Early Times................................          257.81
Cemex (Kosmos) Cement Company Inc.......................          187.47
American Synthetic Rubber Company.......................          136.87
Louisville International Airport........................          136.19
Rohm and Haas Company...................................           28.44
                                                         ---------------
    Total emissions for sources greater than 10 tpy.....   \5\ 38,991.12
Other SO2 sources.......................................           19.24
                                                         ---------------
        Total...........................................       39,010.37
------------------------------------------------------------------------

    The primary SO2-emitting point source located within the
partial county nonattainment area is LG&E's Mill Creek Generating
Station (Mill Creek). Mill Creek consists of four coal-fired boilers
(U1-U4). A breakdown of the actual 2011 emissions by unit in tpy are as
follows: Unit 1--5,211 tpy; Unit 2--6,802 tpy; Unit 3--7,175 tpy and
Unit 4--10,756 tpy. LG&E replaced the existing wet Flue Gas
Desulfurization (FGD) control equipment with more efficient FGD
controls, to comply with the mercury air toxics standard (MATS). These
replacements have been operational for all four units as of June 8,
2016. Mill Creek is the only SO2 point source located in the
partial nonattainment area that is listed in Table 1. Refer to sections
IV.B.4 and IV.C for more information on Mill Creek and the 1-hour
SO2 control strategy.
---------------------------------------------------------------------------

    \5\ The 39,010.37 total SO2 point source emissions in
Table 1 above is the supplemented comprehensive county-level base
year SO2 point source emission inventory. EPA notes that
the Table 1 total county-level 2011 SO2 point source
emissions of 39,010.37 tons differs from the 38,854.87 tons sum of
point source SO2 emissions listed in Table 3 of
Kentucky's 2017 attainment SIP. Table 1 above accounts for EPA's
review of the 2011 NEI v2 for all SO2 point sources in
Jefferson County. The Commonwealth's Table 3 lists all point sources
in the county that emitted over 10 tpy of SO2 which the
Commonwealth acquired from EPA's 2011 NEI v2 on January 31, 2017.
However, the Commonwealth's Table 3 inadvertently omits the
Louisville International Airport point source listed in Table 1
above. Additionally, EPA notes Table 1 above compiles all county-
level SO2 emissions from point sources according to the
2011 NEI v2 including those point sources that emitted less than 10
tpy while Kentucky's Table 3 accounts for those point sources that
emitted greater than 10 tpy as indicated in the 2011 NEI v2. Lastly,
EPA also notes the point source emissions entry in Kentucky's
attainment SIP Table 2 is different from the sum of point source
emissions in Kentucky's Table 3 and EPA's Table 1 total above.
Therefore, the 39,010.37 tons of SO2 for point sources
total in Table 1 above accounts for the comprehensive compilation of
county-level point sources as indicated in the 2011 NEI v2.
---------------------------------------------------------------------------

    Prior to 2016, LG&E Cane Run Generating Station (Cane Run) was the
next largest SO2 source located in the northern portion of
the County and outside the nonattainment area. The facility had three
boilers and reported SO2 emissions of 7,823 tons in 2011. In
2015, LG&E constructed a new natural gas combined cycle turbine (U15)
at the

Cane Run facility and shut-down coal-fired units U4 thru U8 and U10.\6\
---------------------------------------------------------------------------

    \6\ KDAQ submitted information regarding the shut-down of the
coal-fired units U4 thru U8 and U10 and the new natural gas combined
cycle (U15) and auxiliary unit (U16) to EPA on June 20, 2016, to
satisfy part of its obligations under the SO2 Data
Requirements Rule at 40 CFR 51.1203(b). The Title V operating permit
175-00-TV(R2) established a natural gas fuel restriction for EGUs
U15 and U16 is included in the docket for this proposal (ID: EPA-
R04-OAR-2017-0625).
---------------------------------------------------------------------------

    The CEMEX Kosmos Louisville Cement Plant (Kosmos) is outside the
boundary of, but adjacent to, the Jefferson County nonattainment area.
The facility produces Portland and masonry cement and has a production
design capacity of 1.6 million short tons of cement per year. The
primary source of the SO2 emissions are from kiln
operations, which emitted 187 tons in 2011.
    Mill Creek is the only point source in the nonattainment area and
the primary source of the violation at the Watson Lane monitor at the
time of designations for the nonattainment area listed in Table 1.
Therefore, Mill Creek was the only SO2 source the
Commonwealth and the District considered for further evaluation
determined to impact the nonattainment area. Cane Run, Kosmos and the
remaining county-level point sources in Table 1 are all located outside
of the nonattainment area and were accounted for in the attainment
modeling through the background monitor (see section IV.B.4 below).
    KDAQ used the 2011 NEIv2 to obtain estimates of the area and
nonroad sources. For on-road mobile source emissions, KDAQ utilized
EPA's Motor Vehicle Emissions Simulator (MOVES2014) and NONROAD. A more
detailed discussion of the emissions inventory development for the
Jefferson County Area can be found in the June 23, 2017, submittal.
Table 2 below provides Kentucky's 2011 base year county-level
SO2 emission inventory for Jefferson County.

                                            Table 2--2011 Base Year Emissions Inventory for Jefferson County
                                                                          (tpy)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                       Year                              Point           On-road          Nonroad            Area            Event            Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2011..............................................   \7\ 39,010.37            64.20           158.75            38.28             2.61        39,274.21
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Based on an evaluation of county and partial county (nonattainment
area) census and land use data, Kentucky determined that the
nonattainment area accounted for 0.42 percent of the total county land
use \8\ or a total of 1.1 tpy when applied to the county-level source
categories in Table 2, excluding the point source category (see Table 1
above). As noted above, Mill Creek is the only point source in the
nonattainment area. Table 3 below shows the level of SO2
emissions, expressed in tpy, in the partial Jefferson County
nonattainment area for the 2011 base year by emissions source category.
---------------------------------------------------------------------------

    \7\ EPA notes that the total county-level 2011 SO2
point source emissions of 39,010.37 tons differ from the 38,966.95
tons sum of point source SO2 emissions listed in Table 2
of Kentucky's 2017 attainment SIP. Table 2 above accounts for EPA's
review of the 2011 NEI v2 for all SO2 point sources in
Jefferson County.
    \8\ Based on the 2010 census data, the population in Jefferson
County was 741,096 in a land area of approximately 380.42 square
miles. At the census tract level for the county including the
nonattainment area, roughly 8.25 square miles, the population was
estimated to 7,170 or approximately 1 percent of the total county
population. The nonattainment area occupies only 1.61 square miles
of the census tracts or approximately 0.42 percent of the total land
area.

                        Table 3--2011 Base Year Emission Inventory for the Jefferson County Partial Nonattainment Area emissions
                                                                        (tpy) \9\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                     Base year                           Point           On-road          Nonroad            Area            Event            Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2011..............................................  \10\ 29,944.72             0.27             0.67             0.16             0.01        29,945.83
--------------------------------------------------------------------------------------------------------------------------------------------------------

    The attainment demonstration also provides for a projected 2018
attainment year inventory that includes estimated emissions for all
emission sources of SO2 which are determined to impact the
nonattainment area for the year in which the Area is expected to attain
the standard. This inventory should also address any future growth in
the Area or any potential increases in emissions of the pollutant for
which the Jefferson County Area is nonattainment due to the
construction and operation of new major sources, major modifications to
existing sources, or increased minor source activity. KDAQ stated in
its June 23, 2017, submittal that because the Area is rural and
relatively small, it is unlikely that there will be any significant
growth in the nonattainment area. However, the Commonwealth cites to
the District's Regulation 2.04, Construction or Modification of Major
Sources in or Impacting Upon Non-Attainment Areas, which requires NNSR,
approved into the SIP and last updated on October 23, 2001 (see 66 FR
53660). The District's SIP-approved NNSR program requires lowest
achievable emissions rate, offsets, and public participation
requirements for major stationary sources and major modification and
therefore, would account for potential growth in the nonattainment
area. Kentucky reviewed and compiled county-level actual SO2
emissions for all source categories (i.e., point, mobile (on-road and
non-road), area (non-point) and event) in Jefferson County and then
utilized county and partial county nonattainment area population and
land use data to determine estimated SO2 emission
inventories for sources of SO2 in the nonattainment area.
The Commonwealth developed a projected emissions inventory for county-
level SO2 emissions source categories based on the 2011 NEI
as well as the 2008 NEI inventory to extrapolate emissions to 2018. The
point source emissions were estimated by taking credit at Mill Creek
for the new wet FGD controls and title V operating permit limits of
0.20 lb/

MMBtu per unit based on a rolling 30-day average.\11\ Point sources in
the County are still expected to account for approximately 99 percent
of the total county-level SO2 emissions.\12\ Emission
estimates for on-road sources were re-estimated with MOVES2014; nonroad
emissions were projected using national growth factors, and area source
emissions were scaled based on emission factors developed using the
Annual Energy Outlook 2014 for consumption and production forecasts.
Table 4 below provides Kentucky's 2018 projected county-level
SO2 emission inventory for Jefferson County.
---------------------------------------------------------------------------

    \9\ Table 2 of Kentucky's 2017 attainment SIP lists the county-
level emissions. EPA applied the 0.42 percent to the county-level
on-road, nonroad and area source categories in Table 2 to derive the
emissions for the nonattainment area.
    \10\ Mill Creek.
    \11\ Title V operating permit 145-97-TV(R3) issued by Jefferson
County is in the Docket (ID: EPA-R04-OAR-2017-0625) for this
proposal action.
    \12\ Kentucky developed an adjusted 2018 projected attainment
year inventory to account for SO2 emission reductions
from additional point sources in the County including LG&E Mill
Creek and Cane Run. The attainment SIP submission indicates the
SO2 emissions reductions from sources outside of the
nonattainment area are not required to demonstrate attainment but
acknowledges decreases in other source SO2 point source
emissions with the replacement from coal-fired units to other fuel
at LG&E Cane Run, University of Louisville (99 percent decrease),
and Duke Energy's Gallagher Electric Generating Station (92 percent
decrease) in Floyd County, Indiana.

                                  Table 4--2018 Projected Attainment Year SO2 Emissions Inventory for Jefferson County
--------------------------------------------------------------------------------------------------------------------------------------------------------
                       Year                              Point           On-road          Nonroad            Area            Event            Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2018..............................................       18,391.77            38.04           158.75            55.62             5.99        18,650.17
--------------------------------------------------------------------------------------------------------------------------------------------------------

    Based on county and partial county nonattainment area census and
land use data, similar to the base-year nonattainment area inventory,
Kentucky applied the 0.42 percent nonattainment area land use ratio to
the 2018 county-level projected emissions inventory in Table 4
resulting in total of 1.06 tpy for on-road, non-road and area sources,
excluding point source category.\13\ Table 5 below shows the level of
emissions, expressed in tpy, in the Jefferson County nonattainment area
for the 2018 projected attainment year inventory.
---------------------------------------------------------------------------

    \13\ Mill Creek is the only point source in the nonattainment
Area.
---------------------------------------------------------------------------

    KDAQ provided a future year projected emissions inventory for all
known sources included in the 2011 base year inventory, discussed
above. The projected emissions are consistent with expected levels
beyond October 4, 2018, when the control strategy for the attainment
demonstration will be fully implemented. Therefore, as an annual future
year inventory, the point source portion is reasonably estimated beyond
October 4, 2018, and would represent an annual inventory for 2019 or
beyond. The projected emissions in Table 2 are estimated actual
emissions, representing a 55 percent reduction from the base year
SO2 emissions.

                       Table 5--2018 Projected Attainment Year Emissions Inventory for Jefferson County Partial Nonattainment Area
                                                                       (tpy) \14\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                       Year                              Point           On-road          Nonroad            Area            Event            Total
--------------------------------------------------------------------------------------------------------------------------------------------------------
2018..............................................          13,490             0.16             0.67             0.23             0.03        13,491.09
--------------------------------------------------------------------------------------------------------------------------------------------------------

    EPA has evaluated Kentucky's 2011 base year and projected emissions
inventory for the Jefferson County nonattainment area and has made the
preliminary determination that these inventories were developed
consistent with EPA's April 2014 SO2 nonattainment guidance.
Although EPA has noted minor discrepancies between Kentucky's inventory
provided in the nonattainment SIP and the 2011 NEI, EPA is proposing to
find that Kentucky's inventory is sufficiently comprehensive and
accurate to serve the planning purposes for which the inventory is
required. Therefore, EPA is proposing to determine the Jefferson County
SO2 attainment SIP meets the requirements of CAA section
172(c)(3) and (4) for the Jefferson County nonattainment area.
---------------------------------------------------------------------------

    \14\ Table 5 of Kentucky's 2017 attainment SIP lists the county-
level projected emissions. EPA applied the 0.42 percent to the
county-level on-road, nonroad and area source categories in Table 5
to derive the emissions for the partial county nonattainment area.
---------------------------------------------------------------------------

B. Attainment Modeling Demonstration

    The following discussion is an evaluation of various features of
the modeling that Kentucky used in its attainment demonstration.
1. Model Selection
    Kentucky's attainment demonstration used AERMOD, the EPA's
preferred model for this application. The Commonwealth used AERMOD
version 15181 with regulatory default options and a rural land use
designation. Version 15181 of the AERMOD modeling system was the
current regulatory version at the time Kentucky was preparing the
attainment demonstration. Appendix 3 in Kentucky's June 23, 2017,
submittal, provides a summary of the modeling procedures and options,
including details explaining how they applied the Auer technique to
determine that the rural dispersion coefficients were appropriate for
the modeling. Model receptors were located throughout the nonattainment
area using a grid with 100 meters spacing between receptors. Receptor
elevations and hill heights required by AERMOD were determined using
the AERMAP terrain preprocessor version 11103. The meteorological data
was processed using AERMET version 15181 and AERMINUTE version 15272.
The surface characteristics around the meteorological surface station
were determined using AERSURFACE version 13016. An analysis of Good
Engineering Practice (GEP) stack heights and building downwash was
performed using BPIPPRIME version 04274. The results of the downwash
analysis show that the actual stack heights at the Mill Creek facility
exceed the GEP heights, so the GEP stack heights for each stack were
used in the modeling. EPA proposes to find the model selection and
procedures used to run the model appropriate.
2. Meteorological Data
    The Commonwealth incorporated the most recently available five
years of

meteorology data from 2011-2015, as measured at a spatially
representative National Weather Service airport site. The 1-minute
surface-level data came from the Louisville Standiford Field station in
Louisville, Kentucky located about 20 kilometers (km) to the northeast
of the facility. Twice daily upper-air meteorological information came
from the Wilmington Air Park, Wilmington, Ohio station located about
240 km to the northeast. The surface characteristics of the
meteorological surface station were processed using AERSURFACE version
13016 following EPA-recommended procedures and were determined to be
representative of the facility by the Commonwealth. EPA proposes to
find that the meteorological data selection and processing are
appropriate.
3. Emissions Data
    As previously stated, Mill Creek is the only SO2
emitting major point source in the nonattainment area and the only
emission source explicitly modeled in the attainment modeling analysis
for the Jefferson County nonattainment area. All minor area sources and
other major point sources (located outside the nonattainment area
boundary) were accounted for with the background concentration
discussed in Section IV.B.5. Mill Creek operates four coal-fired boiler
units (U1 thru U4) that emit from three stacks. Unit 1 and Unit 2 have
a joint stack (S33) while Unit 3 and Unit 4 have separate stacks (S4
and S34, respectively). Mill Creek replaced its wet FGD Units on all
stacks to improve SO2 reduction efficiencies. All FGD
construction was completed and operational by June 8, 2016.
    The Commonwealth evaluated the emissions from Mill Creek and
derived a set of three SO2 critical emission values (CEVs),
one for each stack, from AERMOD modeling simulations to show compliance
with the 2010 SO2 NAAQS. The AERMOD modeling analysis
resulted in the following CEV's: Stack S33, which serves Units 1 and 2,
was modeled at 225.4 grams/second (g/s) equivalent to 1,789 lb/hr;
stack S4, which serves Unit 3, was modeled at 152.6 g/s equivalent to
1,211 lb/hr; and stack S34, which serves Unit 4, was modeled at 183.6
g/s equivalent to 1,457 lb/hr. In each case, the modeled emission rate
corresponds to 0.29 pounds per million British thermal units (lb/MMBtu)
times the maximum heat input capacity (MMBtu/hr) of the unit(s)
associated with each stack. This form of an emission limit, in lb/
MMBtu, is a frequent form of emission limit associated with electric
generating units. The Commonwealth determined from these AERMOD
modeling simulations that an hourly emission limit of 0.29 lb/MMBtu
would suffice to ensure modeled attainment of the SO2 NAAQS.
However, the Commonwealth opted to apply a 30-day average limit,
following EPA's SO2 nonattainment guidance for setting
longer term average limits. The Commonwealth determined that a 30-day
average limit of 0.20 lb/MMBtu could be considered comparably stringent
to a 1-hour limit of 0.29 lb/MMBtu. Section IV.B.4.ii below, entitled
``Longer Term Average Limits,'' provides more discussion on how the
Commonwealth made this determination.
4. Emission Limits
    An important prerequisite for approval of an attainment plan is
that the emission limits that provide for attainment be quantifiable,
fully-enforceable, replicable, and accountable. See General Preamble at
13567-68. Therefore, part of the review of Kentucky's attainment plan
must address the use of these limits, both with respect to the general
suitability of using such limits for this purpose and with respect to
whether the limits included in the plan have been suitably demonstrated
to provide for attainment. The first subsection that follows addresses
the enforceability of the limits in the plan, and the second subsection
that follows addresses the 30-day average limits.
i. Enforceability
    Section 172(c)(6) provides that emission limits and other control
measures in the attainment SIP shall be enforceable. Kentucky's
attainment SIP for the Jefferson County nonattainment area relies on
control measures and enforceable emission limits for the four coal-
fired boilers at Mill Creek. These emission reduction measures were
accounted for in the attainment modeling for Mill Creek, which
demonstrates attainment for the 2010 SO2 NAAQS. Kentucky's
control strategy for the Jefferson County nonattainment area consists
of replacing FGD control equipment with more efficient FGD controls at
Mill Creek, addressing SO2 emissions for all four units (U1,
U2, U3 and U4): Unit 4 new FGD went into service on December 9, 2014;
Units 1 and 2 new combined FGD went into service on May 27, 2015; and
Unit 3 new FGD went into service on June 8, 2016.
    LG&E installed wet FGD replacements at Mill Creek to comply with
the MATS Rule.\15\ Jefferson County issued a construction permit (No.
34595-12-C) on June 15, 2012, to LG&E authorizing the construction for
wet FGD control equipment replacements for the four coal-fired boilers
at the Mill Creek facility. This construction permit also included a
0.20 lb/MMBtu limit for SO2 as a surrogate for the
hydrochloric acid gas requirements for MATS. This emission limit was
incorporated into the title V permit on July 31, 2014, (145-97-TV
(R2)). LG&E was required to comply with the MATS Rule by April
2016.\16\ Effective June 8, 2016, the Mill Creek facility completed
installation of improved wet FGD SO2 controls on all three
stacks, which has reduced SO2 emissions by approximately 89
percent since 2014 emission levels.\17\
---------------------------------------------------------------------------

    \15\ On December 16, 2011, EPA established the MATS Rule to
reduce emissions of toxic air pollutants for coal or oil power
plants larger than 25 megawatts. The rule establishes alternative
numeric emission standards, including SO2 (as an
alternate to hydrochloric acid), individual non-mercury metal air
toxics (as an alternate to particulate matter (PM)), and total non-
mercury metal air toxics (as an alternate to PM) for certain
subcategories of power plants. CAA section 112, MACT regulations for
coal-and oil fired EGUs, known as the Mercury and Air Toxics
Standards, were targeted at reducing EGU emissions of HAPs (e.g.,
mercury, hydrochloric acid (HCl), hydrogen fluoride (HF), dioxin,
and various metals) and not explicitly targeted at reducing
emissions of SO2. Under the MATS, EGUs meeting specific
criteria may choose to demonstrate compliance with alternative
SO2 emission limits in lieu of demonstrating compliance
with HCl emission limits.
    \16\ Mill Creek was required to comply with the MATS Rule by
April 16, 2016 (extended compliance date).
    \17\ Mill Creek annual SO2 emissions have dropped,
from 28,149 tons in 2014 to 3,040 tons in 2017. See https://ampd.epa.gov/ampd/.
---------------------------------------------------------------------------

    As discussed further in the RACT/RACM section 1V.C below, Kentucky
determined that the wet FGD replacements at Mill Creek provide for
SO2 emission reductions that model attainment for the
Jefferson County nonattainment area. With respect to the 1-hour
SO2 standard, Kentucky established an independent emission
limit of 0.20 lb/MMBtu, for each coal-fired unit at Mill Creek on a 30-
day average basis in accordance with EPA's SO2 nonattainment
guidance for longer term averaging time for the purpose of
demonstrating attainment for the 1-hour SO2 standard (see
section IV.B.4. ii). These emission limits apply independently to each
of the four coal-fired units (U1 thru U4), which emit SO2
from three separate stacks (S33, S4, and S34). Unit 1 and Unit 2 share
a common stack (S33) while Unit 3 and Unit 4 have separate stacks (S4
and S34, respectively). These SO2 limits were established in
a revised title V operating permit 145-97-TV(R3) for Mill Creek

and became effective on April 5, 2017. Mill Creek demonstrates
compliance with the 30-day emission limits through a continuous
emission monitoring system on each stack as well as the monitoring of
the heat input firing rate of each emission unit. The 30-day
SO2 emission limit was established to demonstrate modeled
attainment of the 2010 1-hour SO2 standard for the Jefferson
County nonattainment area and therefore is separate from the
SO2 emission limit of the same numerical value established
to comply with the 2012 MATS Rule (i.e., SO2 as a surrogate
for hydrochloric acid). These two limits were independently established
through unique methodologies and guidance to address distinct and
separate CAA requirements for the LG&E Mill Creek facility. Kentucky
requested that EPA incorporate into the Jefferson County portion of the
Commonwealth's SIP the 30-day SO2 emission limits and
operating and compliance parameters (monitoring, record keeping and
reporting) established at Plant-wide Specific condition S1-Standards,
S2-Monitoring and Record Keeping and S3-Reporting \18\ in title V
permit 145-97-TV(R3).\19\ The accountability of the SO2
emission limits is established through KDAQ's request to include the
limits in the SIP and in the attainment modeling demonstration to
ensure permanent and enforceable emission limitations as necessary to
provide for attainment of the 2010 SO2 NAAQS.
---------------------------------------------------------------------------

    \18\ The plant-wide specific conditions S2-Monitoring and
Recordkeeping and S3-Reporting reference specific compliance
parameters for the 30-day SO2 emission limit for each
individual EGU (U1, U2, U3 and U4). Therefore, the specific
SO2 monitoring and recordkeeping and reporting
requirements, for each EGU are located at the Specific Conditions
S2-Monitoring and Recordkeeping (b) and S3-Reporting (b) for
SO2.
    \19\ EPA notes that Kentucky originally requested that EPA
incorporate into the Kentucky SIP the per unit SO2
emission limits for Mill Creek along with compliance parameters that
were established in title V permit 145-97-TV(R2). However, through a
supplement Louisville has subsequently requested EPA incorporate
portions of permit 145-97-TV(R3) which contains the new 0.20 lb/
mmBtu per unit emission limit based on a 30-day averaging time.
---------------------------------------------------------------------------

ii. Longer Term Average Limits
    Kentucky established an emission limit of 0.20 lb/MMBtu of
SO2 emissions, for each individual coal-fired emission unit
at Mill Creek, on a 30-day average basis. This emission limit applies
individually to each of the four coal-fired units (U1 thru U4), which
emit SO2 from three stacks. Unit 1 and Unit 2 have a joint
stack (Stack ID S33) while Unit 3 and Unit 4 each have separate stacks
(Stack IDs S4 and S34, respectively). As discussed above in the
emissions data section, modeling was performed by Jefferson County and
the Commonwealth to determine an appropriate CEV, in g/s, for each of
the three stacks (stack S33, which serves Units 1 and 2, was modeled at
225.4 g/s; stack S4, which serves Unit 3, was modeled at 152.6 g/s; and
stack S34, which serves Unit 4, was modeled at 183.6 g/s). The
corresponding candidate 1-hour emission factor limits (in lb/MMBtu) may
be calculated by first converting these g/s CEV values to lb/hr (using
a standard unit conversion factor of 1 g/s = 7.937 lb/hr) and then
dividing by the maximum heat input capacity of each unit, in MMBtu/hr.
In each case, the CEV corresponds to an emission factor of 0.29 lb/
MMBtu. Since Units 1 and 2 share a stack (S33), the relevant maximum
heat input capacity was the combined value for both units (6,170 MMBtu/
hr total). Unit 3 has a maximum heat input capacity of 4,204 MMBtu/hr
and vents to a single stack (S4), and Unit 4 has a maximum heat input
capacity of 5,025 MMBtu/hr and vents to a single stack (S34).
    As discussed further below, Kentucky used the procedures in EPA's
April 2014 SO2 nonattainment guidance to determine a
compliance ratio (adjustment factor) of 0.69, which when multiplied by
0.29 lbs/MMBTU yields a 30-day average limit of 0.20 lbs/MMBTU. Each of
the four emission units were subject to this 0.20 lb/MMBtu 30-day
average permit limit effective April 5, 2017. EPA generally defines the
term CEV to mean the 1-hour emission rate for an individual stack that,
in combination with the other CEVs for other relevant stacks, is shown
through proper modeling to yield attainment. As mentioned above,
Kentucky developed a set of CEVs (one per stack) in each case
corresponding to an hourly limit of 0.29 lb/MMBtu and demonstrated with
AERMOD modeling that these CEVs show modeled compliance with the NAAQS.
Unit 1 and Unit 2 have a joint stack (S33) and a combined wet FGD
control, while Unit 3 and Unit 4 have separate stacks (S4 and S34,
respectively), each with individual wet FGD controls.
    EPA's SO2 nonattainment guidance recommends that any
longer term average emission limit should be comparably stringent to
the 1-hour limit that has been shown to provide for attainment of the
2010 SO2 standard. The guidance recommends a procedure,
detailed in Appendix C, for determining an adjustment factor which may
be multiplied times the candidate 1-hour limit to derive a longer term
limit that may be estimated to be comparably stringent to the 1-hour
limit. Using this procedure (discussed in section II above) and using
hourly emission data provided by EPA's Air Markets Program Data
database for Mill Creek for the period 2009-2013 (i.e., before the wet
FGD replacements), Kentucky determined an adjustment factor of 0.69.
Multiplication of this adjustment factor times the candidate 1-hour
limit yielded the 0.20 lb/MMBtu 30-day average permit limit that
Kentucky established in Mill Creek's title V permit effective April 5,
2017. The period from 2009 to 2013 was a period of stable operation
prior to the wet FGD replacements (which were made between late 2014 to
mid-2016), a time when similar but less efficient wet FGDs were used
for SO2 emission control for each coal-fired unit. EPA
believes that these data were the best data available at the time to
Kentucky for estimating the variability of emissions to be expected at
Mill Creek upon compliance with the permit limits. At the time Kentucky
conducted its assessment, only a small amount of post-replacement data
was available. Use of a mix of pre-replacement and post-replacement
data would have yielded a distorted analysis of variability. Therefore,
the 2009 to 2013 data from Mill Creek provided the best representation
available to Kentucky of the variability of emissions to be expected
from this plant.
    Additionally, the 2009-2013 emissions data set yielded an
adjustment factor slightly lower (more conservative) than the average
30-day adjustment factor (0.71) included in Table 1 of Appendix D of
EPA's SO2 nonattainment guidance for emission sources with
wet scrubbers. The results provided in Appendix D were intended to
provide insight into the range of adjustment factors that may be
considered typical. For these reasons, EPA believes the 0.69 adjustment
factor calculated by Kentucky is an appropriate estimate of the degree
of adjustment needed to derive a comparably stringent 30-day average
emission limit for this facility.
    In accordance with EPA's SO2 nonattainment guidance, the
Commonwealth used the distribution of hourly emissions to determine a
corresponding distribution of 30-operating day longer term emission
averages at the end of each operating day. The 99th percentile of the
1-hour average emission values and the 4th maximum value of the 30-day
average emission values \20\ for each year were

calculated, then the average value of the five years' 99th percentile
value was determined. The adjustment factor was calculated as the ratio
of the 99th percentile for the longer term average to the 99th
percentile hourly average emissions for each of the four boilers at
Mill Creek, separately. The adjustment factors for each of the four
units (0.64, 0.68, 0.75 and 0.68) were averaged together to arrive at a
single compliance ratio of 0.69. The average compliance ratio was then
applied to the 0.29 lb/MMBtu hourly emission rate to create a
comparably stringent long term (30-day) emission limit of 0.20 lb/
MMBtu, which was imposed on each emission unit individually. EPA
believes that use of an average adjustment factor is a suitable means
of projecting future variability of the four units at the plant because
the use of an average adjustment factor is likely to yield similar
results to use of unit-specific adjustment factors; indeed, Kentucky
determined that annual potential total SO2 emissions based
on use of an average adjustment factor (with a limit of 0.20 lb/MMBtu
for all units) are about 137 tpy less than would be allowed with limits
of 0.29 lb/MMBtu adjusted by unit-specific adjustment factors.
---------------------------------------------------------------------------

    \20\ EPA notes that the SO2 nonattainment guidance
recommends the compliance ratio be determined based on the 99th
percentile of 30-day values instead of the 4th maximum value used by
Kentucky. Kentucky also computed the compliance ratio using the 99th
percentile and determined that the individual compliance ratios for
each unit did not change because the 99th percentile values are
close to the 4th maximum values.
---------------------------------------------------------------------------

    Based on a review of the Commonwealth's submittal and EPA's
additional analysis described below, EPA believes that the 30-day
average 0.20 lb/MMBtu limit for each of the four boilers at Mill Creek
provides a suitable alternative to establishing a 1-hour average
emission limit for each unit at this source. The Commonwealth has used
a suitable data base and has derived an adjustment factor that yields
an emission limit that has comparable stringency to the 1-hour average
limit that Kentucky determined would otherwise have been necessary to
provide for attainment. While the 30-day rolling average limit allows
occasions in which emissions may be higher than the level that would be
allowed with the 1-hour limit, the Commonwealth'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.
    EPA's SO2 nonattainment guidance recommends evaluating
``whether the longer term average limit, potentially in combination
with other limits, can be expected to constrain emissions sufficiently
so that any occasions of emissions above the critical emission value
will be limited in frequency and magnitude and, if they occur, would
not be expected to result in NAAQS violations.'' For this purpose, EPA
analyzed Air Markets Program Data available from EPA. Mill Creek
completed replacements of the FGD equipment during the period from
December 2014 to June 2016. EPA believes that the emissions data
available after completion of the replacements are the data that best
indicate the likely frequency of hourly emission levels above the
critical emission value. At the time EPA conducted its analysis, these
data were available through the end of March 2018. Therefore, in
addition to the analysis submitted by Kentucky, EPA analyzed hourly
emissions obtained from the EPA Air Markets Program Data for Mill Creek
for the period April 2016 to March 2018,\21\ which encompasses the time
after all the wet FGD replacements were completed and the facility was
operating under a 0.20 lb/MMBtu emission limitation. During this time
Units 1, 2 and 3 did not have any 30-day average values above 0.20 lb/
MMBtu, these units each had only 0.1 percent of the hours exceeding the
``critical emission factor'' of 0.29 lb/MMBtu. Although Unit 4 slightly
exceeded 0.20 lb/MMBtu approximately 5.4 percent of the 30-day averages
during this period (based on Kentucky's compliance determination
procedures), this unit only exceeded the ``critical emission factor''
of 0.29 lb/MMBtu for 0.5 percent of the hours. Therefore, EPA is
proposing to conclude that Mill Creek can reasonably be expected to
exceed the critical emission value only rarely. For details of this
analysis, please refer to the spreadsheet titled ``Mill Creek Analysis
of Values Above the Critical Emission Rate'' in the Docket for this
proposal action.
---------------------------------------------------------------------------

    \21\ FGD replacements were not complete for Unit 3 until June
2016, so the period analyzed for Unit 3 was from July 2016 to March
2018.
---------------------------------------------------------------------------

    For reasons described above and explained in more detail in EPA's
SO2 nonattainment guidance, EPA believes appropriately set
longer term average limits provide a reasonable basis by which
nonattainment plans may provide for attainment. Based on its review of
this information as well as the information in the Commonwealth's plan,
EPA proposes to find that the 30-day average limits for Mill Creek
provide for attainment of the SO2 standard. Furthermore, EPA
notes that 2015-2017 quality-assured and certified design value for the
Watson Lane monitor (AQS ID: AQS ID: 21-11-0051) in the nonattainment
area is 31 ppb, which is below the 1-hour SO2 standard.
    The Commonwealth requested EPA approve into the Jefferson County
portion of the Kentucky SIP, the 30-day, 0.20 lb/MMBtu SO2
emission limit for each boiler as well as operating and compliance
parameters (monitoring and reporting requirements) established in Mill
Creek's title V permit 145-97-TV (R3). EPA has evaluated these
emissions limits and proposes to determine that these limits provide
for attainment of the 2010 SO2 NAAQS.
5. Background Concentration
    Background concentrations of SO2 were included in the
modeling using 2013-2015 season-by-hour monitoring data from the Green
Valley Road monitor (AQS ID: 18-043-1004) located in New Albany,
Indiana. Use of the season-by-hour data is one of the approaches for
calculating background concentrations provided in the SO2
nonattainment guidance. The season-by-hour background values ranged
from 2.13 ppb to 20.67 ppb. This monitor is located approximately 29 km
to the north of the Mill Creek facility in the vicinity of many
SO2 emissions sources, including the Duke Energy Indiana,
LLC, Gallagher Generating Station coal-fired power plant with 3,500 tpy
of SO2 emissions in 2014, which is located approximately 5
km upwind of the monitor. This source, along with other sources in the
area upwind of the monitor (including numerous small area sources in
the City of Louisville and the Louisville Gas and Electric Company,
Cane Run Station power plant), emitted approximately 13,000 tpy of
SO2 in 2014. The background concentrations from the Green
Valley ambient air monitor were used by the Commonwealth to account for
SO2 impacts from all sources besides the Mill Creek
facility, which was explicitly modeled with AERMOD to develop an
appropriate emissions limit. The Commonwealth evaluated other
SO2 monitors in the Louisville area that are closer to the
Mill Creek facility and the nonattainment area, including the Watson
Lane (AQS ID: 21-111-0051), Cannons Lane (AQS ID: 21-111-0067) and
Algonquin Parkway/Firearms Training (AQS ID: 21-111-1041) monitors.
However, the Commonwealth determined that each of these monitors had
issues with data completeness during the 2013-2015 timeframe and thus
were not available for use in their modeling analysis.
    EPA is supplementing the attainment demonstration modeling provided
by the Commonwealth with an independent analysis to assess the
conclusion that the Green Valley background monitor adequately

represents background concentrations of SO2 within this
nonattainment area, including the impact from Kosmos that is located
outside but adjacent to the nonattainment area to the southeast of the
Mill Creek facility. The Commonwealth states in its submission that the
Green Valley monitor was determined to be the most appropriate and
representative background monitor for the demonstration and that it
accounts for impacts from all sources not explicitly modeled, including
Kosmos. As described below, EPA's independent analysis supports KDAQ's
conclusion that the Green Valley monitor adequately represents impacts
from all unmodeled sources including those from Kosmos.
    EPA evaluated whether Kosmos, which is located in close proximity
to the nonattainment area boundary (less than 0.50 km), should be
considered a ``nearby source'' or an ``other source'' as these terms
are defined in Section 8.3.1 of EPA's Guideline contained in 40 CFR
part 51, Appendix W (Appendix W).\22\ Section 8.3.1.a.i of Appendix W
discusses evaluating significant concentration gradient in the vicinity
of the source under consideration for SIP emissions limits for
determining if other sources in the area are adequately represented by
background ambient monitoring. Section 8.3.3.b.ii of Appendix W further
describes the assessment of concentration gradients and states that
``the magnitude of a concentration gradient will be greatest in the
proximity of the source and will generally not be significant at
distances greater than 10 times the height of the stack(s) at that
source without consideration of terrain influences.'' The height of the
cement kiln stack at Kosmos is 75 feet (approximately 23 meters) and
there are no significant terrain features located near Kosmos or within
the nonattainment area boundary. Evaluating the concentration gradients
for Kosmos using the ``10 times stack height'' general rule of thumb
indicates that concentration gradients should be comparatively modest
beyond 230 meters from the stack. The closest edge of the nonattainment
boundary is approximately 480 meters from the stack, which is more than
twice the distance of this general rule of thumb. Therefore, EPA
believes that the SO2 emissions from Kosmos likely would not
result in a significant concentration gradient within the nonattainment
area boundary.
---------------------------------------------------------------------------

    \22\ EPA had previously indicated that Kosmos should be treated
as a ``nearby source.'' This position was communicated to the
Commonwealth in comments on the Prehearing Attainment Demonstration
SIP in a letter dated April 18, 2017. EPA has subsequently performed
additional analysis (discussed later in this section), and believes
that it is appropriate to treat Kosmos as an ``other source,'' which
can be addressed using a representative ambient background
concentration. As an additional measure, Kentucky and Jefferson
County have elected to conduct air quality monitoring to better
characterize the ambient concentrations of SO2 in the
vicinity of the Kosmos facility through an agreed Board Order with
Kosmos. The Board Order, approved by Jefferson County Board on April
19, 2017, requires the facility to deploy an ambient air monitor in
accordance with 40 CFR part 58 and EPA's nonattainment guidance
``SO2 NAAQS Designations Source-Oriented Monitoring
Technical Assistance Document'' (Monitoring TAD February 2016) and
includes a remediation plan indicating if monitored violations of
the NAAQS occur, Kosmos agrees to make changes to their operations
to prevent future violations. EPA Region 4 approved the monitor
location in a letter dated February 1, 2018. Please see the Board
Order located in the Docket for this proposed rule at EPA-R04-OAR-
2017-0625.
---------------------------------------------------------------------------

    EPA also evaluated whether the Green Valley background monitor data
is adequately representative of potential SO2 concentration
impacts from Kosmos within the nonattainment area. This evaluation
consisted of an assessment of wind patterns in the Louisville area, the
SO2 emissions sources in the vicinity of the Green Valley
monitor, and comparing those sources to the Kosmos source. EPA
evaluated wind data from 2011-2015 from the Louisville Standiford Field
Airport to determine the predominant wind patterns. The results of this
analysis show that winds blow predominately from the southeast, south
and southwest directions. EPA then identified significant
SO2 emissions sources located south, southeast and southwest
of the Green Valley monitor. The Commonwealth used Green Valley ambient
concentration data from the 2013-2015 time period for the background
concentrations. Therefore, EPA used SO2 emissions data
contained in the 2014 NEI to evaluate sources in the vicinity of the
Green Valley monitor. EPA's evaluation of sources in the 2014 NEI found
that a large coal fired power plant, the Duke Energy Indiana, LLC,
Gallagher Generating Station, with SO2 emissions of 3,500
tpy, is located approximately 5 km southwest of the Green Valley
monitor. Also, the Louisville Gas and Electric Company, Cane Run
Station reported 8,700 tpy of SO2 emissions in 2014 and is
located approximately 15 km southwest of the Green Valley monitor.
Further, the City of Louisville and its associated numerous small area
SO2 emissions sources (e.g., diesel vehicles and generators)
is located within 9 km southeast of the monitor. Combined, these
sources total over 13,000 tpy of SO2 emissions (according to
the 2014 NEI) located upwind of the monitor and contribute to the
measured SO2 season-by-hour concentrations in 2013-2015 that
ranged from 2.13 ppb to 20.67 ppb.
    EPA used its Emissions Inventory System (EIS) Gateway to obtain
emissions data for Kosmos for comparison to the emissions sources
impacting the Green Valley monitor. The EIS Gateway data for Kosmos
show SO2 emissions of 207 tpy in 2014, 289 tpy in 2015, and
364 tpy in 2016. These emissions data demonstrate that Kosmos'
SO2 emissions are much less than the emissions sources that
are contributing to the measured concentrations at the Green Valley
background monitor. While Kosmos is located much closer to the
nonattainment area boundary (approximately 0.5 km) than the distance
the larger sources of emissions are from the Green Valley monitor (from
5 km to 15 km), the sources near the Green Valley monitor have more
than an order of magnitude more emissions than Kosmos. EPA believes
that the net effect of these compensating differences is that the Green
Valley monitor reasonably indicates the impact of Kosmos on the
nonattainment area.
    Based upon EPA's analyses summarized above, EPA is proposing to
concur with the Commonwealth's use of ambient SO2
concentration data from the Green Valley monitor to account for
potential impacts from Kosmos and all other emissions sources located
outside the nonattainment area that were not explicitly modeled in the
attainment demonstration modeling analysis.
6. Summary of Modeling Results
    The AERMOD modeling resulted in a maximum modeled design value of
190.1 micrograms per cubic meter or 72.6 ppb, including the background
concentration, which is below the 1-hour SO2 NAAQS of 75
ppb. As discussed above, the AERMOD modeling used hourly SO2
emissions for each stack equivalent to the hourly SO2
emission rate of 0.29 lb/MMBtu, which was used to derive the 30-day
average emission limit for the four coal-fired boilers at the Mill
Creek facility. Effective June 8, 2016, the Mill Creek facility
completed installation of improved wet FGD SO2 controls on
all three stacks, and became subject the new 30-day SO2
emission limits on April 5, 2017, which has reduced SO2
emissions by approximately 89 percent from 2014 emission levels.\23\
Furthermore, the Watson Lane

monitoring data trends during the timeframe corroborate the significant
SO2 reductions from Mill Creek facility, supporting EPA's
view that limiting Mill Creek emissions adequately will assure
attainment. EPA has evaluated the modeling procedures, inputs and
results and proposes to find that the results of the Commonwealth's
modeling analysis demonstrate that the limits on Mill Creek assure that
there will be no violations of the NAAQS within the nonattainment area.
---------------------------------------------------------------------------

    \23\ Mill Creek annual SO2 emissions have dropped,
from 28,149 tons in 2014 to 3,040 tons in 2017. See https://ampd.epa.gov/ampd/.
---------------------------------------------------------------------------

C. RACM/RACT

    CAA section 172(c)(1) requires that each attainment plan provide
for the implementation of all RACM 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 RACT)
and shall provide for attainment of the NAAQS. Additionally, 172(c)(6)
require SIPs to contain enforceable emissions limitations and other
control measures to ``provide for attainment'' of the NAAQS. EPA
interprets RACM, including RACT, under section 172, as measures that a
state determines to be reasonably available and which contribute to
attainment as expeditiously as practicable for existing sources in the
area.
    Kentucky's plan for attaining the 1-hour SO2 NAAQS in
the Jefferson County SO2 nonattainment area included a
review of three control measures as potential options which could be
implemented at Mill Creek to reduce ambient SO2
concentrations and attain the SO2 NAAQS: More efficient
scrubber operation; increased stack height; and restriction of high
sulfur fuels. The Commonwealth in coordination with the District
determined that FGD is the appropriate control strategy and represents
RACT/RACM for the nonattainment area. The new controls increase Mill
Creek's ability to control SO2 emissions from previously
permitted levels, i.e., around 90 percent, to a 98 percent removal
rate. Emissions are expected to be reduced from actual emissions of
29,994 tpy in 2011 to a projected post-control level of 13,489.5 tpy.
Effective June 8, 2016, the Mill Creek facility completed installation
of improved wet FGD SO2 controls on all three stacks, and
became subject the new 30-day SO2 emission limits on April
5, 2017 (discussed in section IV.B.4 above). The replaced FGD controls
and April 5, 2017 compliance with the 30-day SO2 emission
limits has resulted in reduced SO2 emissions at Mill Creek
by approximately 89 percent since 2014 emission levels.\24\
Furthermore, the monitoring data trends during the time period
corroborate the existence of the substantial air quality benefits from
the significant SO2 reductions from Mill Creek facility. The
Watson Lane monitor has recorded decreasing SO2
concentrations from an annual 99th percentile value of 148.6 ppb in
2014, 54.2 ppb in 2015, 26.1 ppb in 2016 and 13.7 ppb in 2017.
Currently, the quality-assured and certified 2015-2017, 3-year design
value for the Watson Lane monitor is 31 ppb, which is well below the 1-
hour SO2 standard. In addition to the modeling demonstrating
attainment of the SO2 standard, actual monitored 99th
percentile of 1-hour daily maximum concentrations at the Watson Lane do
not show violations of the NAAQS. On this basis, Jefferson County
determined that no additional measures could contribute to attainment
as expeditiously as practicable. Therefore, the FGD controls for the
Mill Creek Generating Station was determined to constitute RACT/RACM
for the nonattainment area. Kentucky has determined that these measures
suffice to provide for timely attainment. EPA preliminarily concurs
with Kentucky's approach and analysis, and proposes to conclude that
the Commonwealth has satisfied the requirement in section 172(c)(1) and
(6) to adopt and submit all RACT/RACM and emission limitations and
control measures as needed to attain the standard as expeditiously as
practicable.
---------------------------------------------------------------------------

    \24\ According to the CAMD data, Mill Creek annual
SO2 emissions have dropped, from 28,149 tons in 2014 to
3,040 tons in 2017. See https://ampd.epa.gov/ampd/.
---------------------------------------------------------------------------

D. New Source Review (NSR)

    EPA last approved Louisville's NNSR regulations 2.04--Construction
or Modification of Major Sources in or Impacting upon Non-Attainment
Areas (Emissions Offset Requirements) on October 23, 2001 (66 FR
53660). These rules provide for appropriate NSR for SO2
sources undergoing construction or major modification in any
nonattainment area in Jefferson County including the SO2
nonattainment area without need for modification of the approved rules.
Therefore, EPA proposes to conclude that this requirement is met for
this Area through Louisville's existing NSR rules.

E. Reasonable Further Progress (RFP)

    CAA section 172(c)(2) requires attainment plan to require RFP,
which is defined in CAA section 171(1) as ``annual incremental
reductions in emissions of the relevant air pollutant as are required
by this part or may reasonably be required by the Administrator for the
purpose of ensuring attainment of the SO2 NAAQS by the
statutory attainment date.'' For pollutants like SO2 where a
limited number of sources affect air quality, the General Preamble and
the SO2 nonattainment guidance explain that RFP is best
construed as an ambitious compliance schedule. As discussed above, LG&E
completed installation of FGD replacement scrubbers for all four coal-
fired boilers at Mill Creek on June 8, 2016 (Unit 4 new FGD went into
service on December 9, 2014; Units 1 and 2's new FGD went into service
on May 27, 2015; and Unit 3 \25\ new FGD went into service on June 8,
2016) to comply with EPA's MATS extended compliance date of April 16,
2016. However, for purposes of demonstrating attainment of the 2010
SO2 standard, Kentucky established an independent
SO2 emission limit of 0.20 lb/MMBtu for Mill Creek (title V
operating permit 145-97-TV(R3) based on the SO2 emission
reductions from the FGD replacement. All FGD controls are currently
installed and operational at Mill Creek and the facility is currently
complying with the 30-day emission limits as of April 5, 2017 (the date
the revised title V permit was issued).\26\ EPA has evaluated these
emissions limits and proposes to determine that these limits provide
for modeled attainment of the 2010 SO2 NAAQS in the
Jefferson County nonattainment area.
---------------------------------------------------------------------------

    \25\ Unit 3 ceased operation on April 9, 2016, to comply with
the extended MATS compliance date and did not return to service
until all controls and construction necessary to comply with MATS
were completed.
    \26\ See Mill Creek Generating Station title V operating permit
No. 145-97-TV(R3) in the Docket (ID: EPA-R04-OAR-2017-0625) for this
proposal action.
---------------------------------------------------------------------------

    SO2 emissions within the nonattainment area have
decreased approximately 89 percent since 2014, which correlates to a
reduction of SO2 concentrations recorded at the Watson Lane
monitor during this period.\27\ Kentucky finds that this plan requires
the affected sources implement appropriate control measures as
expeditiously as practicable to ensure attainment of the standard by
the applicable attainment date. Mill Creek

has met the limits in Kentucky's plan by the April 5, 2017 compliance
date (effective date of the new 30-day SO2 emission limits).
Therefore, Kentucky concludes that this plan provides for RFP in
accordance with EPA's April 2014 SO2 nonattainment guidance.
Currently, the Watson Lane monitor 2015-2017 quality-assured and
certified SO2 design value is below the 1-hour NAAQS at 31
ppb, EPA expects the Area to show attainment of the 2010 standard by
the statutory attainment date. EPA proposes to concur and concludes
that the plan provides for RFP, as specified in the General Preamble
and the SO2 nonattainment guidance, and therefore satisfies
the requirements of CAA section 172(c)(2).
---------------------------------------------------------------------------

    \27\ According to CAMD data, annual SO2 emissions
have dropped, from 28,149 tons in 2014 to 14,082 tons in 2015.
Subsequent years have reported further reductions with 4,335 tons in
2016 and 3,040 tons in 2017. The Watson Lane monitor (AQS ID: 21-
111-0051), located less than 2 km east of the Mill Creek facility,
recorded decreasing SO2 concentrations from an annual
99th percentile value of 148.6 ppb in 2014, 54.2 ppb in 2015, 26.1
ppb in 2016 and 13.7 ppb in 2017.
---------------------------------------------------------------------------

F. Contingency Measures

    As noted above, EPA's SO2 nonattainment guidance
describes special features of SO2 planning that influence
the suitability of alternative means of addressing the requirement in
section 172(c)(9) for contingency measures for SO2, such
that an appropriate means of satisfying this requirement is for the
Commonwealth to have a comprehensive enforcement program that
identifies sources of violations of the SO2 NAAQS and to
undertake an aggressive follow-up for compliance and enforcement.
Kentucky's plan provides for satisfying the contingency measure
requirement in this manner. Jefferson County is authorized by Kentucky
Revised Statutes Chapter 77 to ensure that control strategies,
including reasonably achievable control technology and contingency
measures, necessary to attain the standard by the applicable attainment
date are implemented in the nonattainment area. Kentucky's proposed SIP
revision has been developed in accordance with this authority. In
addition, if a monitored exceedance of the SO2 NAAQS occurs
in the future and all sources are found to comply with applicable SIP
and permit emission limits, Jefferson County will perform the necessary
analysis to determine the cause of the exceedance, and determine what
additional control measures are necessary to impose on the Area's
stationary sources to continue to maintain attainment of the
SO2 NAAQS. Jefferson County will inform any affected
stationary sources of SO2 of the potential need for
additional control measures. If there is a violation of the NAAQS for
SO2 within the nonattainment area, then Jefferson County
will notify the stationary source that the potential exists for a NAAQS
violation. Within six months of notification, the source must submit a
detailed plan of action specifying additional control measures to be
implemented no later than 18 months after the notification. The
additional control measures will be submitted to the EPA for approval
and incorporation into the SIP. EPA preliminarily concurs and proposes
to approve Kentucky's plan for meeting the contingency measure
requirement as described above and in the proposed SIP revision.

V. 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 into the Jefferson County portion of the Kentucky SIP, a
SO2 emission limit and specified compliance conditions
established in title V permit 145-97-TV(R3) for each coal-fired
emissions unit at the LG&E Mill Creek Generating station in Jefferson
County nonattainment area. Specifically, EPA is proposing to
incorporate into the Jefferson County portion of the Kentucky SIP a
0.20 lb/MMBtu 30-day SO2 emission limit for each EGU (U1,
U2, U3 and U4) and operating and compliance conditions (monitoring,
recordkeeping and reporting) all established at Plant-wide Specific
condition S1-Standards, S2-Monitoring and Record Keeping and S3-
Reporting in title V permit 145-97-TV(R3) for EGU U1, U2, U3 and U4.
The SO2 emission standards specified in the permit are the
basis for the attainment demonstration. EPA has made, and will continue
to make, these materials generally available through
www.regulations.gov and at EPA Region 4 office (please contact the
person identified in the For Further Information Contact section of
this preamble for more information).

VI. EPA's Proposed Action

    EPA is proposing to approve Kentucky's SO2 nonattainment
SIP submission, which the Commonwealth submitted to EPA on June 23,
2017, for attaining the 2010 1-hour SO2 NAAQS for the
Jefferson County nonattainment area and for meeting other nonattainment
area planning requirements. EPA has preliminarily determined that the
nonattainment SIP meets the applicable requirements of sections 110,
172, 191 and 192 of the CAA and nonattainment regulatory requirements
at 40 CFR part 51. This SO2 nonattainment plan includes
Kentucky's attainment demonstration for the Jefferson County
nonattainment area and other nonattainment requirements for RFP, RACT/
RACM, NNSR, base-year and projection-year emission inventories,
enforceable emission limits and control measures and compliance
parameters, and contingency measures. Additionally, EPA is proposing to
approve into the Jefferson County portion of the Kentucky SIP, Mill
Creek's enforceable SO2 emission limits and compliance
parameters (monitoring and reporting) established at Plant-wide
Specific condition S1-Standards, S2-Monitoring and Record Keeping and
S3-Reporting established in title V permit 145-97-TV(R3).

VII. Statutory and Executive Orders

    Under the CAA, the Administrator is required to approve a SIP
submission that complies with the provisions of the Act and applicable
Federal regulations. See 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. This action merely
proposes to approve 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);
     Is not an Executive Order 13771 (82 FR 9339, February 2,
2017) regulatory action because SIP approvals are exempted under
Executive Order 12866;
     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 (Public Law 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 CAA; 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).
    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 as specified by Executive Order 13175 (65
FR 67249, November 9, 2000), nor will it impose substantial direct
costs on tribal governments or preempt tribal law.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by
Reference, Intergovernmental relations, Reporting and recordkeeping
requirements, Sulfur oxides.

    Authority: 42 U.S.C. 7401 et seq.

    Dated: November 1, 2018.
Onis ``Trey'' Glenn, III,
Regional Administrator, Region 4.
[FR Doc. 2018-24582 Filed 11-8-18; 8:45 am]
 BILLING CODE 6560-50-P