[Federal Register Volume 76, Number 66 (Wednesday, April 6, 2011)]
[Rules and Regulations]
[Pages 18870-18893]
[FR Doc No: 2011-8032]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R04-OAR-2005-AL-0002-201047; FRL-9290-3]

Approval and Promulgation of Implementation Plans: Alabama: Final
Disapproval of Revisions to the Visible Emissions Rule

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: EPA is taking final action to amend an October 15, 2008, final
rulemaking on two State Implementation Plan (SIP) revisions regarding
the State of Alabama's rules for visible emissions from certain
stationary sources. EPA has now determined upon reconsideration that
Alabama's SIP revisions, dated September 11, 2003, and August 22, 2008,
are not approvable pursuant to the Clean Air Act (CAA or Act) section
110(l). Accordingly, EPA is disapproving the two SIP revisions provided
to EPA by the State of Alabama, through the Alabama Department of
Environmental Management (ADEM), dated September 11, 2003, and August
22, 2008 (Submittals). No further action is required by Alabama because
the SIP revisions were not required by the CAA. As a result of this
action, Alabama's visible emissions rule that was in the SIP prior to
the October 15, 2008, final action will be the current SIP-approved
rule as of the effective date of this action. EPA urges Alabama to
undertake rulemaking that will bring its State-effective rule into
conformance with its SIP-approved rule.

DATES: Effective Date: This rule will be effective May 6, 2011.

ADDRESSES: EPA has established a docket for this action under Docket
Identification No. EPA-R04-OAR-2005-AL-0002. All documents in the
docket are listed on the http://www.regulations.gov index. Although
listed in the index, some information is not publicly available, i.e.,
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Certain other material, such as
copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy form. Publicly available docket
materials are available either electronically through http://www.regulations.gov or in hard copy at the Regulatory Development
Section, Air Planning Branch, Air, Pesticides and Toxics Management
Division, U.S. Environmental Protection Agency, Region 4, 61 Forsyth
Street, SW., Atlanta, Georgia 30303-8960. EPA requests that, if at all
possible, you contact the person listed in the FOR FURTHER INFORMATION
CONTACT section to schedule your inspection. The Regional Office's
official hours of business are Monday through Friday, 8:30 to 4:30,
excluding federal holidays.

FOR FURTHER INFORMATION CONTACT: Ms. Lynorae Benjamin, Chief,
Regulatory Development Section, Air Planning Branch, Air, Pesticides
and Toxics Management Division, Region 4, U.S. Environmental Protection
Agency, 61 Forsyth Street, SW., Atlanta, Georgia 30303-8960. The
telephone number is<PHONE_NUMBER>. Ms. Benjamin can also be reached
via electronic mail at<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION:

Table of Contents

I. What is the background for this action?
II. What action is EPA taking and what is EPA's rationale for
disapproving the submittals?
III. Response to Comments
IV. Final Action
V. Statutory and Executive Order Reviews

I. What is the background for this action?

    This action follows three key EPA actions regarding Alabama's
request for approval of the two visible emissions SIP revisions. The
first was an October 15, 2008, final rule (73 FR 60957) approving
revisions to the Alabama SIP embodied in two submittals dated September
11, 2003, and August 22, 2008 (Submittals). The second was an April 3,
2009, action granting a February 25, 2009, petition for reconsideration
on the October 15, 2008, final action which had approved the SIP
revisions. The third was an October 2, 2009, proposed rule (74 FR
50930) identifying two alternative options being considered by EPA as
part of the reconsideration process (the alternative proposals were
either to affirm the October 15, 2008, rulemaking, thereby approving
Alabama's Submittals or to amend the October 15, 2008, rulemaking,
thereby disapproving Alabama's Submittals). EPA has now determined that
Alabama's Submittals are not approvable pursuant to CAA section 110(l).
Detailed background information for this action is available in the
proposed rulemaking published on October 2, 2009. 74 FR 50930.
    In relevant but brief part, on September 11, 2003, ADEM submitted a
voluntary \1\ request for EPA approval of a SIP revision (2003
Submittal) containing proposed revisions to the existing EPA-approved
visible emissions portion of the Alabama SIP, found at Alabama
Administrative Code (AAC) 335-3-4-.01, ``Visible Emissions,'' and
pertaining to sources of particulate matter (PM) emissions.\2\ In

an action published on April 12, 2007 (72 FR 18428), EPA proposed to
approve the 2003 Submittal contingent upon the State of Alabama
submitting a revised SIP submittal addressing EPA's concerns regarding
impacts of the rule changes on attainment of the National Ambient Air
Quality Standards (NAAQS), as set forth in 72 FR 18428-18434. EPA's
proposal notice explained that the State would have to provide EPA with
a revised SIP submittal consistent with certain changes described by
EPA in the April 12, 2007, notice of proposed rulemaking before EPA
could approve the revisions. The proposal notice also described EPA's
rationale for requesting the additional submittal. Specifically, EPA
noted that the 2003 Submittal was not approvable because the revision
``would allow a source to emit at a higher allowable average opacity
percent level (as measured by a COMS--Continuous Opacity Monitoring
System--in six-minute increments) on a quarterly basis as well as
allowing higher short term excursions than the current approved SIP
allows.'' 72 FR at 18430/3. EPA further explained that ``in the absence
of a supporting demonstration of compliance with the CAA requirements
from the State, we believe that the 2003 SIP submittal is not
approvable as submitted.'' Id.
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    \1\ The request was ``voluntary'' because it was not
specifically required by the CAA or its implementing regulations,
rather, ADEM chose to revise its rules and submit the SIP revision.
    \2\ PM particles with an aerodynamic diameter less than or equal
to a nominal 10 micrometers are referred to as PM10; PM
particles with an aerodynamic diameter less than or equal to a
nominal 2.5 micrometers are referred to as PM2.5. As a
general matter, the term ``PM'' refers to particulate matter of
unspecified size range and includes both PM10 and
PM2.5.
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    On August 22, 2008, Alabama, through ADEM, provided EPA with an
amended submittal (2008 Submittal). After further evaluation, EPA
determined that it could approve the Submittals (i.e., the 2003
Submittal as amended by the 2008 Submittal). On October 15, 2008, EPA
took final action to incorporate into the Alabama SIP, the revisions to
Alabama's visible emissions rule included in the Submittals. 73 FR
60957. EPA's rationale for its approval is discussed in that final
action. In order to approve the Submittals in 2008, EPA relied on two
main findings: ``(1) The revision would not increase the allowable
average opacity levels; and (2) the relationship between changes in
opacity and increases or decreases in ambient PM2.5 levels
cannot be quantified readily for the sources subject to this SIP
revision, and is particularly uncertain for short-term analyses.'' 73
FR 60959/2. The October 15, 2008, final action was effective on
November 14, 2008 (by its terms, the Alabama rule change became
effective, and thus applicable to sources, on May 14, 2009).
    Following the October 2008 final action, EPA received two petitions
for reconsideration submitted on behalf of the Alabama Environmental
Council (AEC) and other parties (Petitioners), one on December 12,
2008, and one on February 25, 2009. EPA considered these petitions
under section 553(e) of the Administrative Procedures Act (APA) and the
CAA. The first petition for reconsideration raised procedural and
substantive concerns with EPA's October 15, 2008, final action.\3\ EPA
denied the December 12, 2008, petition via letter on January 15, 2009.
The second petition incorporated by reference the issues raised in the
first petition and also identified additional substantive and
procedural concerns not included in the first petition.\4\ EPA granted
the Petitioners' second request for reconsideration of the October 15,
2008, final action via letter on April 3, 2009. In that letter, EPA
explained that it anticipated initiating a new rulemaking process to
provide additional opportunities for public comment.
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    \3\ The Petitioners raised eight main issues: (1) EPA was
arbitrary and capricious in failing to reopen the public comment
period when ADEM made changes to the rule after the close of the
public comment period; (2) EPA was arbitrary and capricious in
deviating from rulemaking policy regarding documentation of post-
comment period meetings between EPA and ADEM and failing to meet
with Petitioners in addition to ADEM; (3) EPA was arbitrary and
capricious in proposing to approve a SIP revision before the rule
had even been developed at the State level; (4) EPA failed to comply
with rulemaking procedures by failing to complete the docket prior
to finalizing the rulemaking package; (5) the rule should not have
been approved because it does not represent reasonably available
control technology requirements for SIPs because Alabama has
nonattainment areas for PM2.5; (6) EPA's approval of the
rule is not consistent with either Section 110(l) or 193 of the CAA
due to likely increases in short-term particulate matter emissions;
(7) EPA's final action is not consistent with EPA policies on excess
emissions and director's discretion; and (8) the final rule does not
comply with 40 CFR Part 51 because it is not an ``appropriate''
visible emission limitation.
    \4\ The Petitioners specifically highlighted two new issues: (1)
The DC Circuit's decision in Sierra Club v. EPA, 551 F.3d 1019 (D.C.
Cir. 2008) (SSM MACT decision) made the Agency's action on the SIP
revision untenable; and (2) new documents added to the docket show
that throughout the consideration of this matter, EPA acted in an
arbitrary and duplicitous manner in failing to re-notice the
rulemaking for public comment given the differences between what EPA
required of Alabama in the April 12, 2007, proposal and what Alabama
actually submitted for approval in its August 22, 2008, submittal.
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    On December 12, 2008, Petitioners filed a lawsuit in the Eleventh
Circuit Court of Appeals challenging EPA's October 15, 2008, final
action. EPA and the appellants subsequently jointly stayed the
litigation pending the conclusion of EPA's reconsideration process.
EPA's October 2, 2009, proposed rule was EPA's initiation of a new
rulemaking process to reconsider its prior action on the Submittals. In
that proposal, EPA articulated two alternative options and sought
public comment on both. One option was to affirm the October 15, 2008,
final action (thus approving the Submittals) and the other was to amend
the October 15, 2008, final action (thus disapproving the Submittals).
The bases for each alternative were described in detail in the October
2, 2009, proposed rulemaking. 74 FR at 50932-50934. The responses to
the comments EPA received on the October 2, 2009, proposed action are
summarized in section III of this rulemaking.

II. What action is EPA taking and what is EPA's rationale for
disapproving the submittals?

    EPA is now taking final action to amend its October 15, 2008, final
action and to disapprove Alabama's 2003 and 2008 SIP Submittals
regarding its visible emissions rule. As EPA explained in its October
2, 2009, proposed rulemaking, the primary issue for resolution is
whether approval of the Submittals is consistent with the requirements
of the CAA, specifically, the requirements of section 110(l). If the
approval were appropriate under section 110(l), EPA would need to
consider whether it would also meet the requirements of section 193,
given that the visible emissions rules in question were in effect prior
to November 15, 1990, and apply to some sources that are located in
areas designated nonattainment for one or more NAAQS. In light of the
fact that this SIP revision would apply statewide, including
nonattainment areas, EPA has concluded that it cannot approve the SIP
revision under section 110(l) if it would worsen air quality by
allowing increased emissions of criteria pollutants or precursors to
such criteria pollutants. In particular, if the revision would result
in increases in emissions of pollutants for which an area is designated
nonattainment, specifically PM2.5, EPA considers that
allowing increased emissions of such pollutants would interfere with
the area's ability to attain the NAAQS.\5\ See, e.g., 70 FR 53

(January 3, 2005); 70 FR 28429 (May 18, 2005) (previous rulemaking
actions addressing section 110(l)).
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    \5\ With respect to attainment areas, section 110(l) requires
that an approvable SIP revision not interfere with maintenance of
the NAAQS or any other requirement of the CAA. In some
circumstances, allowing increases in criteria pollutants may not
interfere with maintenance of the NAAQS. EPA has not analyzed
whether this SIP revision would be approvable with respect to
attainment areas only because the Submittals included rules that
applied throughout Alabama, which includes both attainment and
nonattainment areas, and the State did not make a showing that
emissions from such sources would not interfere with maintenance of
the NAAQS in attainment areas and with attainment of the NAAQS in
nearby nonattainment areas. Similarly, EPA is not basing this
decision on section 193 because the Submittals are not approvable
under section 110(l); however, section 193 would have to be
addressed before EPA could consider approval of the revisions.
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    In this particular circumstance, the analysis of whether the
Submittals satisfy the CAA is made more difficult by the uncertainty in
the precise relationship between the opacity of a stack emission stream
and the mass of PM in the same emission stream at the affected sources.
After consideration of all the issues raised by the Petitioners in
their February 2009 petition for reconsideration, as well as comments
received on the October 2, 2009, proposed rulemaking from many industry
groups, individual companies, state agencies, and other non-
governmental organizations, EPA has concluded that disapproving the
2003 and 2008 Submittals results in the interpretation of the CAA that
is most consistent with the plain text and legislative history of the
CAA, as well as the air quality goals set forth in the CAA. What
follows is EPA's explanation of its analysis, which involves a
discussion of the following: (1) The role of visible emissions in NAAQS
attainment and maintenance; (2) the history of Alabama's visible
emissions rule; (3) consideration of CAA section 110(l); (4) comparison
of the original rule to the revised SIP-approved rule; (5) the role of
uncertainty in EPA's analysis; and (6) the types of information that
would be particularly useful in developing a visible emissions SIP
revision.

1. Role of Visible Emissions in NAAQS Attainment and Maintenance

    Opacity may be defined as the degree to which emissions reduce the
transmission of light and obscure the view of an object in the
background. 40 CFR 60.2. Opacity is important because it provides
information regarding pollutants visible to the eye leaving an
emissions source. In general, the more that opaque particles pass
through an emissions point, the more light will be blocked, thus
increasing the opacity percentage. However, variables such as the size,
number, and composition of the particles in the emissions can result in
variations in the percentage of opacity.
    Historically, visible emissions have been an important tool for
implementation of PM NAAQS and, in particular, for the implementation
and enforcement of PM limits on sources to help attain the NAAQS.
Visible emissions have been a useful tool to indicate overall operation
and maintenance (O & M) of a facility and its emissions control devices
even before modern instruments that measure PM on a direct, continuous
basis existed. The observation of greater than normal visible
emissions, particularly on a recurring basis, has served as an
indication that incomplete combustion or other changes to the process
and/or the control device had or were occurring; such changes
frequently led to increased PM emissions. Although opacity is not a
criteria pollutant, opacity standards continue to be used as an
indicator of the effectiveness of emission controls for PM emissions,
or to assist with implementation and enforcement of PM emission
standards for purposes of attaining PM NAAQS. Opacity measurements can
serve as an indicator of a well-maintained, well-operated source and
that such sources should be able to achieve visible emissions that
comply with opacity limits. For example, data submitted by one
commenter show routine source operation with opacity of about five
percent.\6\ Conversely, visible emissions at much higher percentages
(such as those allowed by Alabama's revised rules), particularly on a
recurring basis, may indicate that a source is in violation of
applicable SIP or permit mass limits as well.
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    \6\ Alabama Power Company in Attachment T from the docket shows
that over a three-year period its units did not exceed 5 percent
opacity for 55.4 percent of the operating time, 10 percent opacity
for 89 percent of the operating time, and 15 percent opacity for
97.6 percent of the operating time. In addition, the U.S. District
Court for the Northern District of Alabama found in 2009 that at
TVA's Plant Colbert, Units 1-4 typical baseline opacity measured
about 5-8 percent during normal unit operation, and Unit 5 was
projected to operate below 5 percent opacity even with a partially
malfunctioning control device and below 10 percent ``under extreme
conditions that are unlikely to ever occur.'' Sierra Club v. TVA,
592 F. Supp. 2d 1357, 1367 (N.D. AL 2009).
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    Many commenters agreed that the precise relationship between
opacity and PM emissions was uncertain. Despite this uncertainty, there
is a general relationship between opacity and particulate matter mass
emissions. As a result, increases in opacity can be indicative of
changes in emissions control device performance or source operation,
which in turn can lead to increases in mass emissions.
    Furthermore, based on the information contained in the record for
this action and a general lack of opacity and corresponding PM
emissions data received to date, it is apparent that the mass of
emissions based on short-term increases in opacity cannot be quantified
readily for each of the 19 sources affected by the SIP revisions in the
Alabama Submittals.\7\ There are several contributors to the
uncertainties associated with relating mass emissions to increases in
opacity, including: (1) Differences between combustion technology
characteristics and fuel components; (2) differences in control
technology types, temperatures at which they operate, and load
characteristics; (3) the recognition that both opacity and mass
emissions are subject to significant variability over short periods of
time and fluctuations such that one may act independently of the other;
and (4) differences between the mass of particles that exists at the
point of opacity measurement by the COMS (e.g., in the stack) and the
direct PM2.5 that forms immediately upon exiting the stack
(that are related to fuel components more than to control technology).
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    \7\ EPA specifically requested that commenters provide any
available concurrent data showing the PM mass emissions and opacity
for sources affected by the SIP revision at issue, but no commenter
supplied this information. 74 FR 50934.
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2. History of Alabama's Visible Emissions Rule

    EPA first approved Alabama's visible emissions rules into the
Alabama SIP in 1972. 37 FR 10842, 10847 (May 31, 1972). The State
submitted the visible emissions rules as part of its SIP for attainment
and maintenance of the total suspended particulates (TSP) NAAQS (the
predecessor to the PM NAAQS). The State has revised these rules three
times in support of those goals.
    Historically, Alabama has had areas with attainment problems for
the various PM NAAQS. Originally, EPA designated some areas in Alabama
as nonattainment for the TSP NAAQS. In 1987, EPA replaced the TSP NAAQS
with the PM10 NAAQS, and all areas of Alabama were
designated as attainment for those NAAQS. 56 FR 11101 and 58 FR 67734.
All areas of Alabama remain designated attainment for the
PM10 NAAQS. In 1997, EPA promulgated new annual and 24-hour
particulate matter NAAQS, using PM2.5 as the indicator.
Effective April 5, 2005, EPA designated portions of Alabama, in the
Birmingham and Chattanooga areas, as nonattainment for the 1997
PM2.5 NAAQS. 70 FR 944. In 2006, EPA promulgated new
PM2.5 NAAQS, significantly tightening the 24-hour standards.
Effective December 14, 2009, the Birmingham area was designated
nonattainment for the 24-hour PM2.5

NAAQS, as revised in 2006. The Birmingham area remains designated as
nonattainment for both the 2006 24-hour and 1997 annual
PM2.5 NAAQS. Chattanooga remains designated as nonattainment
for the 1997 annual PM2.5 NAAQS. Alabama's visible emissions
rules continue to be a part of the Alabama SIP for attainment and
maintenance of the PM NAAQS.
    The SIP revision at issue affects the applicable visible emissions
limits at approximately 19 stationary source facilities.\8\ These 19
facilities include older coal-fired utilities, cement manufacturing
facilities, and pulp and paper facilities, among others. Five of these
facilities are located in or near nonattainment areas for the current
PM2.5 NAAQS. Specifically, Cheney Lime and Cement Company
(Allgood), Ernest C. Gaston Electric Generating Plant (Alabama Power
Company (APC)), and William Crawford Gorgas Electric Generating Plant
(APC) are located within the Birmingham nonattainment area for the 1997
annual and 2006 24-hour PM2.5 NAAQS; Bowater Incorporated
(Westover) is located near that area. In addition, Widows Creek Fossil
Plant (Tennessee Valley Authority (TVA)) is located in the Chattanooga
nonattainment area for the 1997 annual PM2.5 NAAQS. Other
facilities affected by these visible emissions rules may also impact
these or other nonattainment areas.
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    \8\ At this time, it is EPA's understanding that the rules at
issue apply to 19 facilities. Due to the applicability portions of
the rule, the rule could apply to fewer facilities over time, but
will not likely apply to any more.
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    The geographic location of affected sources covered by the visible
emission rules in the EPA-approved SIP is relevant. This is because (as
is discussed more fully below) EPA interprets section 110(l) to
prohibit approval of SIP revisions that would increase emissions of
pollutants for which an area is designated nonattainment, in the
absence of offsetting emission reductions or an attainment
demonstration addressing the rule changes at issue.
    Opacity remains an important tool that states and EPA rely upon in
establishing and enforcing PM-related standards for SIPs and other
standards promulgated under the CAA (such as New Source Performance
Standards (NSPS) and National Emission Standards for Hazardous Air
Pollutants). For example, opacity measurements can serve as an
indicator of compliance with PM emissions between PM stack tests. The
Submittals would provide sources with the flexibility to allow for
visible emissions of up to 100 percent opacity (previous maximum
opacity was 40 percent) for up to 2.4 consecutive hours per day \9\
(previous consecutive maximum time for ``exempt'' periods per day was 6
minutes). This change, like all SIP revisions, must be consistent with
section 110(l).
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    \9\ The Submittals allow up to 2.4 hours per day of operation at
opacity levels in excess of 20 percent, provided that the total of
such periods did not exceed 2 percent of operating time in a
quarter, excluding periods of startup, shutdown, load change and
rate change (or other short intermittent periods upon terms approved
by ADEM's Director and included in a State-issued permit).
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3. Consideration of CAA Section 110(l) \10\
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    \10\ EPA's evaluation of this SIP revision focused on section
110(l). If EPA were to find the revision approvable under section
110(l) it would have to consider other issues raised by the
commenters, including whether it is approvable under section 193.
Further, section 110(l) applies with respect to all NAAQS in effect,
even where EPA has not yet made designations.
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    In considering whether to approve the SIP revision at issue in this
action, EPA must evaluate the changes embodied in the Submittals from
the State in light of the requirements of section 110(l). Section
110(l) of the CAA provides, in relevant part, that:

    * * * The Administrator shall not approve a revision of a plan
if the revision would interfere with any applicable requirement
concerning attainment and reasonable further progress (as defined in
section 7501 of this title), or any other applicable requirement of
this chapter.

    Congress added section 110(l) during the 1990 amendments to the CAA
as support for the cornerstone of the SIP program in the CAA--the
attainment and maintenance of the NAAQS. 101 Stat. 2404 (101 Pub. L.
549) (November 15, 1990). The provision was added as part of general
revisions to section 110 to address EPA actions on SIP revisions, in
part responding to court cases such as a Ninth Circuit Court of Appeals
case, Abramowitz v. EPA, 832 F.2d 1071 (9th Cir. 1987), which discussed
Train v. NRDC, 421 US 60 (1975) (both cases addressed EPA consideration
of SIP revisions in light of some evaluation of whether the revision at
issue would affect the NAAQS, i.e., the impacts upon attainment or
maintenance of the NAAQS). S. Rep. No. 101-228 (Report of the Committee
on Environment and Public Works, United States Senate) (1990 CAA Legis.
Hist. 8338, 8360-8363).
    By its plain language, section 110(l) applies to every SIP revision
submitted by a state. In evaluating whether a given SIP revision would
interfere with attainment or maintenance, as required by section
110(l), EPA generally considers whether the SIP revision will allow for
an increase in actual emissions into the air over what is allowed under
the existing EPA-approved SIP. EPA has not required that a state
produce a new complete attainment demonstration in order to make every
revision to its SIP, provided that the status quo air quality is
preserved. For the Submittals at issue in this action, EPA's view has
been that if the SIP revision does not interfere with attainment or
maintenance of the NAAQS, then it is unlikely to interfere with other
applicable requirements. For example, if EPA concludes that emissions
of PM allowed under the SIP are not increasing as a result of the SIP
revision, then no additional control requirements would be required
under section 193.
    EPA has historically interpreted section 110(l) as requiring the
Administrator to have some basis on which to conclude that a SIP
revision would not interfere with attainment and maintenance of the
NAAQS, or any other applicable requirement, before EPA could approve
the SIP revision. EPA has regularly requested such information from the
state to support a revision, particularly where there was some
uncertainty regarding the impacts of the SIP revision. For example, in
2005, the State of North Carolina submitted a SIP revision that raised
issues similar to the Alabama proposal. After considerable discussion
between EPA and North Carolina about what revisions would be consistent
with the requirements of section 110(l), the State submitted a SIP
revision that addressed key issues. The rules in the revision retained
the same number of total minutes and maximum levels of opacity allowed
during excursion periods as under the prior EPA-approved SIP (i.e., the
four hourly six minute exceedance periods allowed under the existing
North Carolina SIP could occur at any time, including consecutively,
during a 24-hour period, but the allowable maximum opacity levels
during these periods was not increased). In particular, EPA did not
adopt an ``average daily opacity'' approach for North Carolina, which
would have allowed extended periods of high opacity (in excess of 40
percent). See 70 FR 61556 (October 25, 2005). Similarly, EPA has
proposed to disapprove a visible emissions SIP revision for Ohio in
which that state sought to relax limitations on the number of occasions
of excess opacity per hour, potentially allowing entire days with
elevated opacity. The revision was submitted without a section 110(l)
showing that the relaxation in opacity requirements would not reflect
increased emissions

that would interfere with attainment and maintenance of the NAAQS or
other requirements of the CAA. 70 FR 36901 (June 27, 2005).
    EPA recognizes that 110(l) analyses are case-specific and that the
scope and nature of the analysis will vary, depending on the factual
details of the SIP revision at issue. See, e.g., Hall v. EPA, 273 F.3d
1146 (9th Cir. 2001) and Kentucky Resources Council, Inc., v. EPA, 467
F.3d 986 (6th Cir. 2006); see also, 61 FR 16,050, 16,051 (April 11,
1996) (actions on which the Kentucky Resources Council case were
based).\11\ However, in the absence of a full attainment or maintenance
demonstration, EPA has consistently required a sufficient basis in the
record for concluding that the SIP revision would not interfere with
attainment and maintenance of the NAAQS, or any other applicable CAA
requirement.\12\
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    \11\ EPA's action today is consistent with both these 9th and
6th Circuit cases addressing 110(l).
    \12\ As is discussed below, EPA's previous approval of the
Submittals was a departure from this approach.
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4. Comparison of the Original Rule to the Revised Rule

    The substantive starting point for evaluating any SIP revision is
to consider the differences between the current EPA-approved SIP rule
and the revised rules being proposed by the state in the revision. Many
of these differences were highlighted by the Petitioners and other
parties during the public comment process on both the April 2007
proposal and the October 2, 2009, reconsideration proposal.
    In this case, we began our analysis by comparing the rule in effect
in the Alabama SIP at the time of EPA's April 2007 proposed action
(hereafter ``the previous rule'') with the 2003 and 2008 Submittals
(hereafter ``the current rule''). Under both rules, the maximum number
of exempt six-minute periods \13\ allowed per day is the same--24; the
maximum ``allowable average quarterly opacity'' \14\ is approximately
the same--22 percent under the previous rule, and 21.6 percent under
the current rule; and the maximum ``allowable average daily opacity''
is the same under both rules--22 percent.\15\ However, there are two
significant differences \16\ between the previous rule and the current
rule. The first is that the current rule allows for maximum visible
emissions of 100 percent opacity during the exempt periods, while the
previous rule allowed for maximum visible emissions of only 40 percent
opacity during such periods. AAC 335-3-4-.01(4) (current rule). The
second is that the current rule allows exceedances of the 20 percent
SIP standard for intervals of up to 2.4 consecutive hours (i.e., up to
24 consecutive six-minute periods per calendar day), while the previous
rule allowed exceedances of the 20 percent SIP standard for intervals
of only 0.1 consecutive hours (i.e., one six-minute period per
hour).\17\ Thus, the two key differences are that the current rule
allows for opacity to increase up to 100 percent and allows up to 2.4
consecutive hours of opacity at that level (i.e., the ``bundling'' of
high opacity periods) per day. A critical question, therefore, is
whether the significant increase of the maximum allowable opacity from
40 percent to 100 percent for such extended periods could result in
more PM emissions were sources to take advantage of the changed limits.
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    \13\ Unless otherwise noted, this notice refers to exempt
periods other than those provided by the previous rule for startup,
shutdown, load change and rate change (or other short intermittent
periods upon terms approved by ADEM's Director and included in a
State-issued permit), which were part of the existing SIP-approved
rule and remained unchanged under the October 15, 2008 final action
rule.
    \14\ ``Allowable average quarterly opacity'' is not a
traditional measurement used by states or EPA for monitoring opacity
or for opacity standard-setting purposes. Rather, EPA first used
this approach, which allows sources to ``average out'' periods of
very high opacity with periods of lower opacity, in the notice
proposing to approve the Submittals, if the rules were changed to
limit allowable average quarterly opacity. See 72 FR 18432
(providing instructions for calculating ``allowable average
quarterly opacity levels.'') Subsequently, in the notice approving
the Submittals, EPA also used the concept of ``allowable average
daily opacity.'' 73 FR 60958.
    \15\ See previous rule AAC 335-3-4-.01(1)(b) and current rule
AAC 335-3-4-.01(4) and 335-3-4-.01(5).
    \16\ One of the technical support documents (TSDs) provided for
this action explains in detail the differences between the current
and prior visible emissions rules. EPA considered all the
differences in reaching its decision today. EPA is simply
identifying two significant differences that are particularly
relevant to the analysis of the submittal.
    \17\ See previous rule AAC. 335-3-4-.01(1)(b) and current rule
AAC 335-3-4-.01(4).
---------------------------------------------------------------------------

    In EPA's original approval notice, we adopted a limited analytical
framework for addressing this question. We did not conclude that the
proposed change in the SIP would not result in increased PM emissions.
Rather, we established a new metric of ``average daily opacity'' (and
``average quarterly opacity'') and concluded that section 110(l) did
not prohibit approval of a SIP revision that allowed significantly
increased opacity levels for longer consecutive periods of time because
the revision would not increase the allowable average opacity levels
(on either a quarterly or daily basis). This analysis was focused on
opacity and operational conditions regarding opacity as opposed to a
focus on the relationship between opacity and PM mass emissions, in
part because EPA did not have any useful source-specific data regarding
the relationship between opacity and PM mass emissions at the affected
facilities.
    EPA also concluded that the relationship between changes in opacity
and increases or decreases in ambient PM2.5 levels could not
be quantified readily for the sources subject to the SIP revision, and
was particularly uncertain for short-term analyses and that the level
of uncertainty about whether increased opacity levels allowed under the
revision would allow increased mass emissions was sufficiently high
that, in the absence of additional information to confirm a change in
emissions one way or the other, section 110(l) did not prohibit
approval of the SIP revision.
    After reconsideration, however, EPA's position is that both of the
findings that provided the foundation for its initial approval of the
SIP revision were not strong enough to support approval under the CAA.
EPA concludes that, as it was described in the Submittals, the concept
of ``average daily opacity'' is not a useful tool for evaluating
whether the Submittals are likely to maintain current air quality,
particularly given the lack of other limitations on opacity exceedances
in the Submittals. One of the primary purposes of opacity limits is to
ensure that PM control devices are operating within normal parameters.
Thus, larger and longer exceedances of an opacity limit (e.g., 100
percent opacity or other high opacity levels over a longer period of
time such as 2.4 consecutive hours), which may indicate problems with a
control device or other significant changes in emissions, are more
significant than shorter and smaller exceedances. Under the approach of
the revised rule, a control device could temporarily shutdown or
malfunction, potentially resulting in 100 percent opacity, for an hour
or two and the source could still be in compliance with the 22 percent
average daily limit. By contrast, an opacity limit that requires
consistent compliance at 20 percent, and allows only one excursion of
six minutes per hour to 40 percent opacity will limit larger and longer
excursions.
    In addition, an opacity limit that requires consistent compliance
at 20 percent and allows only one excursion of six minutes per hour to
40 percent opacity helps ensure that sources and their control devices
are properly maintained, operated, and controlled. In EPA's experience,
a source that is properly maintained, operated and

controlled should be capable of meeting the opacity requirements of the
Alabama SIP without this revision. EPA is concerned that the allowance
of higher levels and longer consecutive durations of opacity
exceedances, even with an ``average daily opacity'' cap, would
undermine an important purpose of the opacity limit, to ensure proper O
& M of sources and their control devices.
    After reviewing the issues raised in the petition for
reconsideration and additional information received during the
reconsideration public comment period, EPA concludes that the approach
utilized to evaluate the Submittals in the October 15, 2008, rulemaking
resulted in a fundamentally incomplete analysis. Requiring a source to
maintain an average daily opacity of 22 percent does not provide
assurance that the source will generally achieve the same level of PM
control (and emissions) as a source which meets a limit of 20 percent
opacity, except for one six-minute period per hour at 40 percent.
Accordingly, the approach of the prior notice, which focused solely on
maintaining an overall average daily (and quarterly) opacity does not
provide an adequate framework for assessing the impact of the
Submittals on emissions and air quality, which is the touchstone of the
analysis required under section 110(l).
    EPA did receive modeling from a variety of sources (which is
discussed in the Response to Comments portion of today's action,
beginning with Comment 19) which attempt to show the impact on air
quality from the changes to the opacity requirements in the Submittals.
In addition to EPA's discussion in the Response to Comments section,
EPA's Technical Support Document addressing the modeling identifies the
information gaps that prevented EPA from conducting the type of source-
specific analysis that would be necessary for completion of an adequate
110(l) evaluation. For example, elements that are missing from the
submitted modeling include: data from all the sources and source
categories affected by the Alabama Submittals; a demonstration of the
relationship between PM emissions and opacity at a particular facility
and source-category; consideration of emissions from other sources in
the modeled area; condensable PM data; explanation for background PM
levels used in the evaluation; and an explanation of the use of
PM10 as a surrogate for PM2.5; among other
concerns. As EPA noted in its evaluation of modeling submitted during
the first comment period:

    Although source-specific correlations between opacity and mass
emissions can be established for some sources, none have been for
the sources subject to this SIP revision and therefore assumptions
must be made about how a change in the opacity rule might affect the
level of PM mass emissions being modeled. These assumptions made
about the relationship drive model results and, thus, are important
in evaluating the result of the modeling exercise.

73 FR 60961. EPA has carefully reviewed all of the modeling submitted
and has concluded that, without source-specific data on the mass-
opacity relationship, there is not an adequate basis to model the
impact of the revisions to the opacity rules on PM mass emissions.
Therefore, the models are insufficient and too inaccurate to provide a
basis for concluding that the Submittals satisfy the requirements of
section 110(l). As discussed below, EPA would need additional data and
information before it could conclude that this approach would not
result in an increase of nonattainment pollutants that would interfere
with attainment and maintenance of the NAAQS.

5. The Role of Uncertainty in EPA's Analysis

    As was noted earlier, a key issue in evaluating the Submittals is
the element of uncertainty in the relationship between opacity and PM
mass emissions. Many SIP submittals involve some level of uncertainty.
EPA has never, and does not now, take the position that a small
possibility that an attainment SIP might turn out not to result in
attainment of the NAAQS, or to prevent a violation of the NAAQS, or
that a SIP revision might worsen air quality, necessitates denial of a
SIP revision. EPA recognizes that attainment planning generally
requires a high degree of technical judgment, and often involves some
degree of uncertainty. In EPA's prior approval, we concluded that the
level of uncertainty concerning the impact of the SIP revisions on
emissions of PM from sources was so great that EPA could not make a
technical judgment as to whether or not approval of the Submittals
would likely interfere with attainment and maintenance of the NAAQS or
any other applicable requirements. In the face of such uncertainty, EPA
concluded that section 110(l) did not prohibit the approval of the
revisions at issue. After reconsideration, EPA has concluded that its
traditional, and more precautionary, approach to interpreting section
110(l) is appropriate.
    There is a general relationship between opacity and PM emissions
such that an increase in opacity means the concentration of smaller
particles, larger particles, or both, increases. See, e.g., Malm,
William C., ``Introduction to Visibility,'' Cooperative Institute for
Research in the Atmosphere, May 1999 at Chap. 2, p. 8. However, because
increases in the quantity of smaller particles may be accompanied by
decreases in the quantity of larger particles, and vice versa, changes
in opacity do not necessarily reflect corresponding changes in the mass
of PM emissions. While source-specific relationships between opacity
and PM emissions may be obtained through testing, they can be
influenced by a variety of circumstances such as fuel compositions and
types of equipment malfunction that may occur. Therefore, while changes
in opacity generally indicate changes in PM emissions, there is
uncertainty about quantifying the specific level of PM emissions
associated with varying levels of opacity.
    EPA has previously explained the elements of that uncertainty in
its proposed reconsideration action. 74 FR at 50933. One key element is
the recognition that both opacity and mass emissions are subject to
significant variability of short periods of time and fluctuations such
that one may act independently of the other. Id. Thus, EPA concludes
(and many commenters also acknowledged) that there is a relationship
between opacity and PM such that periods of high opacity can result in
increased PM emissions, which in turn can cause or contribute to a PM
NAAQS violation. We can say with certainty that periods of high opacity
would cause interference with the PM NAAQS in some circumstances. What
EPA does not know is precisely when such changes in opacity would cause
the interference, particularly for a variety of source types. This is
the unknown element discussed in detail in EPA's proposal and this
final action.
    Section 110(l) was intended to allow SIP revisions in the absence
of full attainment demonstrations, but EPA's view is that Congress
would not have wanted EPA to approve SIP revisions where EPA lacked not
only an attainment demonstration but also any basis for concluding that
the SIP revision would not interfere with attainment or maintenance of
the NAAQS, and other applicable requirements. Accordingly, consistent
with our past practice in considering SIP revisions, EPA concludes that
there must be either a contemporaneous attainment demonstration or some
other basis for concluding that a SIP revision will not interfere with
attainment, and that uncertainty alone is not a sufficient

basis for approving a SIP revision. Moreover, EPA has also concluded,
following reconsideration, that there is a sufficient likelihood that
the SIP revision at issue in this action could allow increased mass
emissions over what would have been allowed under the previously
approved SIP rule and that, in the absence of additional information or
limitations, the revision is not approvable under section 110(l). As
noted by commenters during the reconsideration process, although a
precise correlation between mass emissions and opacity for an
individual source can be difficult to ascertain, the changes
contemplated in the Submittals are such that changes in emissions,
including increases, are possible under the opacity levels allowed by
the SIP revision. Given the location of affected sources within
nonattainment areas, EPA has concluded that additional emissions from
such sources would interfere with attainment and maintenance of the
NAAQS in these areas.
    EPA recognizes that there are circumstances in which a source will
record opacity levels in excess of a 20 percent standard without
necessarily increasing its mass emissions, but there are also many
circumstances where increased opacity levels are associated with
increased mass levels. The Submittals would provide sources with the
flexibility to allow for visible emissions of up to 100 percent opacity
for up to 2.4 consecutive hours per day. The degree of operational
flexibility associated with the Submittals is such that EPA concludes
that the opacity limits in the Submittals are likely overall to allow
increased PM emissions. Even though every instance of operation at
greater than 20 percent opacity may not result in increased emissions,
and though EPA cannot precisely quantify the effect of approving the
Submittals on the information in the record, it is reasonably
foreseeable that approving the Alabama Submittals would allow increased
mass emissions, for at least some sources and under at least some
conditions, over the PM emission levels that would have been allowed
under the previously approved SIP rule. Given this situation, section
110(l) requires disapproval of the Submittals absent additional
limitations which would significantly diminish the likelihood that mass
emissions increases will occur. The result of the disapproval is simply
that Alabama's previous EPA-approved visible emissions rule will become
the federally-enforceable rule in the SIP (although EPA urges that
Alabama take any regulatory action necessary to avoid having a State-
effective rule that is different from the SIP-approved rule).

6. Information Regarding Development of Visible Emissions SIP Revisions

    In EPA's October 2, 2009, reconsideration proposal following
reconsideration, EPA included a section entitled, ``III. What
Additional Information Would EPA Like To Receive?'' 74 FR 50934. EPA
specifically requested information on the nature of the relationship
between opacity and PM mass emissions over both the short and long term
and when the opacity and PM mass emissions may have a predictable
relationship to one another. Id. EPA also requested source-specific
data from Alabama facilities affected by the Submittals. EPA also
included a bulleted list of more specific types of information that
could assist in conducting an analysis on the impacts of a SIP revision
on the air quality of the affected area (i.e., a 110(l) analysis). Id.
Providing guidance on development of a general visible emissions SIP
revision is difficult because opacity and visible emissions are most
easily evaluated in a source-specific context. However, states may
consider the following information useful.
    As a general matter, states may find it instructive to look at
visible emissions SIP revisions that EPA has approved. An example is
the North Carolina approval previously referenced in this rulemaking.
70 FR 61556. As was noted earlier in this rulemaking, there are two key
differences between the North Carolina action and the Alabama
Submittals now being disapproved. First, the North Carolina action did
not allow additional minutes of opacity exceptions. Second, the North
Carolina action did not change the percentage of opacity allowed during
the exception periods.
    More generally, EPA expects that providing assurance that a source
will comply with a rule that allows no more than one 6-minute
exceedance per hour and opacity readings no greater than 40 percent
clearly requires more effective control equipment and/or operating
procedures than it takes to assure a source will comply with a rule
that allows longer consecutive periods of exempt opacity excursions and
at higher opacity levels. Opacity and PM emissions are related closely
enough that control equipment effective enough to meet the more
stringent opacity standard (in terms of the number of consecutive
excursions allowed and the level of opacity excursions allowed) will
also provide a greater level of PM emissions control. Due to the
importance of first understanding the relationship between opacity and
PM emissions at the affected sources, source-specific SIP revisions
have historically been used by most states in developing different
visible emissions standards for a source, particularly when those
standards are less stringent than existing standards. Source-specific
SIP revisions allow for the ability to analyze the PM/opacity
relationship and establish an appropriate opacity limit that will not
impact the NAAQS. The technical analysis for such rule changes would
likely involve collection of parallel mass and opacity data for the
source in question. If that information indicates that there will be
increases in PM mass emissions or opacity, then further analysis would
be required to ensure that the increased emissions associated with the
increased opacity (or rule change at issue) will not interfere with
attainment, reasonable further progress, or any other applicable
requirement of the CAA (the 110(l) factors), for that particular source
and locale. Further, a more definitive modeling assessment of the
effect of any proposed rule would include the representative range of
emission rates and/or conditions producing 100 percent opacity for each
type of source affected by the rule.
    When source-specific information is available, the uncertainty
about the relationship between opacity and mass, and the implication of
the changes in opacity on PM emissions, is reduced and there may be a
basis upon which to make an informed judgment about the impacts of the
change with respect to section 110(l). Further, source-specific actions
are much more discrete since they typically apply at a particular unit
of a particular facility, thus eliminating the need to evaluate the
statewide impact of the change. EPA has undertaken source-specific
opacity revisions. See, e.g., 66 FR 33027 (June 20, 2001) (approving a
source-specific revision affecting 14 units in Alaska). Similarly, a
focus on a particular source category may also allow for more specific
understanding regarding the relationship between opacity and PM
emissions at the affected facilities and the rule's overall impact to
air quality. 73 FR 36485 (June 27, 2008) (proposing disapproval of
source-category specific revision; notice explains how a source-
category revision may be developed).
    EPA is not suggesting that every revision to an opacity standard
requires source-specific analyses. If a submission provides a
sufficient basis for EPA to conclude that changes to a visible
emissions requirement will not result in

increased PM emissions in a nonattainment area over what would have
been allowed under the previously approved SIP rule (or otherwise
interfere with any applicable requirement of the CAA), then EPA
anticipates that it would be approvable under section 110(l).
Ultimately, the key issue that must be addressed in any 110(l) analysis
of an opacity SIP revision is an evaluation regarding the impact of
that revision on PM emissions and the NAAQS. As was noted earlier,
because Alabama's Submittals were voluntary revisions to the SIP and
not mandated, Alabama has no obligation to develop another visible
emissions revision.

III. Response to Comments

    The following are EPA's responses to the significant adverse
comments on EPA's October 2, 2009, proposal. EPA is obligated to
respond to adverse comments received and thus, has reviewed the
comments that were adverse to a disapproval of the State's SIP
revisions. EPA is now responding to those comments. Many of the
comments overlapped or were redundant, so in order to assist with
readability of the responses, we have organized the comments and
responses into subject-matter groupings identified below.

1. Basis for Reconsidering the 2008 Final Action
2. Relationship Between Opacity and PM Emissions
3. Modeling
4. Relative Stringency of Previous Rule (Pre-2008 Final Action) to
Current Rule (Post-2008 Final Action)
5. Attainment and Maintenance of the PM NAAQS (PM10 and
PM2.5) and Data Submitted in Response to October 2009
Reconsideration Proposal
6. Impact of Uncertainty in These SIP Revisions
7. Applicability of CAA Sections 110(l) and 193 to This Action
8. CAA Section 110(l) ``Demonstration'' of Non-Interference With the
NAAQS and Other Requirements
9. Use of COMS and Need for Exemptions
10. Relationship of SIP Revisions to 40 CFR Section 51.212
11. Relationship of SIP Revisions to the Compliance Assurance
Monitoring (CAM) Rule
12. Relationship of SIP Revisions to Sierra Club v. EPA, 551 F.3d 1019
(D.C. Cir. 2008), and the Vacatur of Certain Provisions in 40 CFR Part
63
13. Relationship of SIP Revisions to Reasonably Available Control
Technology (RACT)
14. Other Exemptions in the Alabama SIP Related to Visible Emissions

1. Basis for Reconsidering the 2008 Final Action

    Comment 1. Commenters argued that because EPA's October 2, 2009,
reconsideration proposal notice did not select an option, or at least
disclose to the public which option EPA preferred, EPA's interpretation
of the relevant CAA provisions and their application to the situation
here will be entitled to no deference upon judicial review. Also, the
commenters asserted that their ability to comment on the proposal is
hamstrung by EPA's failure to articulate which option EPA would choose.
    Response 1. EPA does not agree with commenters' characterization of
the October 2, 2009, proposed rulemaking. That proposal described two
alternative actions in detail--including the technical, legal, and
policy bases for each of the respective actions. EPA provided
sufficient information for each alternative for commenters to
participate meaningfully and for either alternative proposal to be
finalized, depending upon what additional information was developed as
a result of the reconsideration. EPA has previously used the
alternative proposal option when dealing with a particularly complex
rulemaking (see, e.g., proposal regarding California-Imperial Valley
Planning Area, 66 FR 42187 (August 10, 2001)). In this case, EPA's
interest in ensuring public comment on the two primary options was best
achieved through the alternative proposals. There is no indication of
any commenter being unable to provide meaningful comments. Numerous
commenters provided substantive comments on both of the two proposals.
The substance of the commenters' own comments reflect that they were on
notice of the factual and legal issues relevant to the reconsideration.
    Comment 2. Commenters asserted that there is no new record evidence
provided by EPA, Petitioners, or other interested parties in order to
support the second petition for reconsideration of EPA's approval of
the SIP revision in the October 2008 final action.
    Response 2. EPA's authority to reconsider a SIP rulemaking derives
from both the Administrative Procedures Act (APA) section 553(e) as
well as authority in the CAA. The APA provides the opportunity for any
person to ``petition for the issuance, amendment, or repeal of a
rule.'' 5 U.S.C. 553(e). The APA does not explicitly limit this right
based on new evidence or any other limitations alleged by commenter.
Even if there were such a limitation, EPA disagrees that the second
petition for reconsideration did not raise issues that warranted
reexamination of the factual and legal basis for the October 2008
action.
    Comment 3. Commenters argued that the CAA does not authorize EPA to
continue to entertain petitions for reconsideration ``indefinitely''
after a specific CAA process has been followed and reconsideration has
been denied. According to the commenters, the CAA allows EPA to
``call'' an approved State SIP for legal deficiencies, but does not
allow EPA to continue to reconsider its actions on a state-submitted
SIP revision after the revision is approved. Commenters also argued
that EPA lacks authority to reverse its approval of the SIP revisions
because EPA may only change its standard for review of SIP revisions
under section 110(l) prospectively--i.e., EPA may only apply an
allegedly new reading of section 110(l) to new state requests for SIP
revision. The commenters further argued that any request for
reconsideration of a final SIP approval must follow the procedures
identified in CAA section 110(k)(5) for seeking a change to a
previously approved SIP revision (noting that section 307 does not
apply and section 553(e) of the APA cannot be used to bypass 110(k)).
    Response 3. EPA disagrees with the commenters' views of EPA's
authority to reconsider rulemakings under these circumstances. An
administrative agency has the authority to reconsider its decisions,
unless Congress specifically limits the agency's discretion to do so.
See, e.g., Gun South, Inc. v. Brady, 877 F.2d 858, 862 (11th Cir. 1989)
(holding that agencies have implied authority to reconsider and rectify
errors even though the applicable statute and rules do not provide
expressly for such reconsideration). The DC Circuit Court recently
affirmed this authority in New Jersey v. EPA, 517 F.3d 574 (D.C. Cir.
2008), where it explained that an agency normally can change its
position and reverse a prior decision but that in the case before it,
Congress limited EPA's ability to remove sources from the list of
hazardous air pollutant source categories, once listed, by requiring
EPA to follow the specific delisting process at CAA section 112(c)(9).
See also, e.g., Trujillo v. General Electric Co., 621 F.2d 1084, 1086
(10th Cir. 1980) (``Administrative agencies have an inherent authority
to reconsider their own decisions, since the power to decide in the
first instance carries with it the power to reconsider''). EPA recently
applied this approach in connection with California conformity

SIPs. EPA had approved the SIPs based on a mobile source model that was
current at the time of EPA's approval. EPA proceeded to update the
mobile source model, but under the previous SIP approvals, conformity
decisions would continue to be made on the basis of those previous SIP
approvals, and would not take into account the updates to the mobile
source model. To remedy this problem, EPA conducted a rulemaking that
revised the previous SIP approvals so that they were limited to the
period before States submitted, and EPA found adequate, the mobile
source budgets in new SIPs based upon the update of the mobile source
model. See 74 FR 55292, 55342 (October 27, 2009) (discussing EPA's
inherent authority to reconsider SIP actions). See also 73 FR 21528
(August 22, 2008) (EPA final action on reconsideration of previous
Georgia SIP action).
    The commenters questioned EPA's authority to reconsider a SIP
action and appear to suggest that EPA's authority is limited to only a
SIP ``call'' under section 110(k)(5) of the CAA. The SIP call process,
however, is a distinct and separate authority that Congress has given
to EPA for use when EPA determines that a current SIP is substantially
inadequate to attain or maintain compliance with the CAA requirements.
See, e.g., Sierra Club v. Georgia Power Company, 443 F.3d 1346, 1348
(11th Cir. 2006) (describing the separate revision provisions under the
CAA and the SIP call process generally). The SIP call process was not
intended to be the sole means of revising the SIP and does not displace
EPA's authority to reconsider its approval.\18\ While the two processes
may be complementary, the authority to reconsider an action and the
authority to issue a SIP call are not mutually exclusive, and one or
the other may be appropriate in different circumstances.
---------------------------------------------------------------------------

    \18\ In addition to its SIP call provisions, the CAA also
includes provisions for the correction of errors in the SIP. See CAA
section 110(k)(6). EPA notes that the process it has used for
reconsidering and disapproving this SIP revision is entirely
consistent with the process required under section 110(k)(6).
---------------------------------------------------------------------------

    As the commenters correctly noted, EPA's approval of a SIP revision
is not subject to the rulemaking requirements of the CAA section 307(d)
because it does not fall within the enumerated categories in section
307(d)(1) of the CAA. Section 307(b)(1), to which a SIP revision
rulemaking is subject, contemplates the ``filing of a petition for
reconsideration by the Administrator of any otherwise final rule or
action.'' 42 U.S.C. 7607(b)(1). Courts have also found that EPA must
follow the rulemaking requirements of the APA when evaluating a SIP
submission (see, e.g., Hall, 273 F.3d at 1161), including section
553(e). Finally, the very nature of a SIP is that it is not a static
document; it is regularly revised to account for new EPA standards and
new emissions reduction technologies. 42 U.S.C. 7410(a)(2)(H).
    Furthermore, EPA notes that the SIP revision at issue did not take
effect by its own terms until after the date on which EPA granted the
second petition for reconsideration. No sources affected by the
revisions to the Alabama SIP should have been required to alter their
facilities or their operations in reliance on the prior EPA approval.
EPA's view is that a source that is properly maintained, operated and
controlled should have no difficulty complying with either the pre-
existing or the revised version of visible emissions rules in the SIP,
or even complying simultaneously with both versions of the SIP, which
suggests that the reconsideration process should not have been
disruptive for any source. In the present case, EPA concluded that
reconsideration of its approval of the Submittals was necessary to
ensure that the final decision was consistent with the plain text and
legislative history, and air quality goals of the CAA, given the facts
at issue in this situation. While the result of EPA's action today is
that Alabama's Submittals are disapproved, the effective date for such
disapprovals will be the effective date of this final action. Thus,
there is nothing retroactive about today's final action.
    Comment 4. Commenters argued that if EPA reverses its approval of
the Submittals now, that would be arbitrary, contrary to EPA's
statutory authority and its responsibility to implement the CAA, and in
violation of EPA's ``delegation commitment'' to Alabama under the CAA.
    Response 4. As a point of clarification, Alabama is authorized to
implement certain portions of the CAA through its SIP. Commenters do
not explain the ``delegation commitment'' reference. Such terminology
is inapposite as the majority of CAA programs are ``authorized,'' not
``delegated,'' particularly with regard to those embodied in a SIP.
Some CAA programs, such as section 112, are routinely ``delegated'' by
EPA to states; however, section 112 programs are not SIP programs.
EPA's responsibility to implement the CAA extends to ensuring that its
decisions are based in the CAA and its implementing regulations. In the
instant action, EPA is reversing a previous approval decision because
after reconsideration, EPA has concluded that a disapproval is required
based on known technical information (as opposed to uncertainty) and an
interpretation of section 110(l) that is most consistent with the plain
text and legislative history of the CAA, as well as the air quality
goals set forth in the CAA. As was explained above, EPA's
reconsideration process is well grounded in statutory authority.
    Comment 5. Commenters asserted that EPA's reconsideration proposal
notice does not provide any information about the legal authority that
the Agency believes justifies its action. The commenters further argued
that it is incumbent upon the Agency to disclose the legal basis upon
which it proposes to act and to provide the public with the opportunity
to comment on that asserted basis, and that without such an explanation
from EPA, the October 2, 2009, proposal notice is deficient and does
not provide an adequate basis upon which the Agency can lawfully take
action.
    Response 5. EPA does not agree with commenters' assessment. The
October 2, 2009, reconsideration proposal includes two alternative
options for final action--both based upon application of section 110(l)
of the CAA. Section 110(l) applies to all SIP revisions and limits
EPA's legal authority to approve revisions to existing EPA-approved SIP
provisions. The reconsideration proposal notice explained the
alternative proposed actions as well as the interpretation of section
110(l) that would support each of the alternatives. The substance of
the comments reflects that the commenters were in fact on notice of the
factual and legal issues that EPA raised for reconsideration.
    Comment 6. Commenters asserted that certain documents received in
response to a Freedom of Information Act (FOIA) request do not support
the reopening of the public comment period.
    Response 6. As was explained earlier, there is no prohibition on
EPA's authority to review a final action and allow for a new public
comment period on that action. EPA has provided the basis of the
reconsideration of the October 15, 2008, final rule--the CAA and the
APA. Whether documents obtained through a FOIA support EPA's
reconsideration, in the opinion of the commenter, is not relevant.
    Comment 7. Commenters asserted that EPA appears to be considering a
``policy change'' in how it interprets and applies section 110(l) in
the reconsideration process. Commenters argued that if EPA wants the
State to amend its approved SIP to reflect revised EPA policy on
section 110(l), EPA must act under section 110(k)(5) of the CAA and not
through a ``unilateral'' notice and

comment process. Commenters asserted that they are aware of no other
situation where EPA has proposed to act in this manner to ``withdraw''
a final approval of a SIP revision.\19\
---------------------------------------------------------------------------

    \19\ EPA notes APC's request that should EPA take final acting
disapproving Alabama's SIP revisions, that EPA stay its disapproval
action pending litigation (APC Comments, pp. 10, footnote 2). EPA is
not acting on this request through this final action.
---------------------------------------------------------------------------

    Response 7. EPA's interpretation of 110(l) that is outlined in this
final action is consistent with EPA's historic interpretation of
110(l), the plain text of the CAA, and the legislative history of the
CAA (as well as court opinions that have considered 110(l)). EPA's
decision is based on its re-evaluation of the likelihood that approval
of the Submittals will result in increases of allowable PM emissions.
In amending its previous action, EPA is placing greater weight on the
technical aspects of the SIP Submittals that are known to have the
potential for adverse impacts on the NAAQS as a result of allowing
greater levels and durations of opacity exceedances. This change does
not represent a policy shift, but rather, an analytical reconsideration
of what decision is most supported by the CAA, given the facts at issue
in this rulemaking. Moreover, EPA's reconsideration process in this
action was far from ``unilateral.'' By reopening the rulemaking for
additional public comment, and setting forth the legal, technical, and
policy bases for that alternative outcomes in the reconsideration
process, EPA sought to ensure that the public had an opportunity to
comment and review the possible options.
    Ironically, if anything, the SIP call process apparently preferred
by commenters is more ``unilateral'' in that such a process is
initiated after EPA has concerns that an existing SIP is substantially
inadequate and often requires a state to take action to revise its SIP
following EPA's final action on the SIP call. Here, EPA's disapproval
will result in a rule coming back into effect that was in effect for
years. Alabama will not be required to submit a revised SIP revision.
Further, as explained above, EPA has used the alternative proposal
approach in the past. While the approach is not appropriate in all
regulatory actions, it serves an important purpose of seeking public
comment in the unusual circumstance in which two potentially
supportable decisions exist and additional information or input from
the public may be helpful to EPA in making a final decision.
    Comment 8. Commenters stated that EPA's prior analysis of the SIP
revision remains sound and that there is no basis for reversing the
conclusions of that analysis. According to the commenters, the rigors
of the prior SIP revision process insured that the concerns raised by
the Petitioners have already been heard and considered by both ADEM and
EPA multiple times. The commenters argued that the petition for
reconsideration raised no issues that were not or could not have been
raised during the prior rulemaking process. Therefore, the commenters
argued that reversing the prior approval of Alabama's Submittals at
this point and in this manner would not only be an abuse of EPA's
authority under the CAA, it would be the height of arbitrary and
capricious Agency action.
    Response 8. EPA does not agree with the commenters' assessment. For
the reasons described in this final notice, EPA has determined that
reconsidering its prior approval and seeking additional notice and
comment on the factual and legal issues raised by the Petitioners was
an appropriate action. In reversing its prior approval, EPA has
concluded that disapproval is necessary pursuant to the plain text of
the CAA, its legislative history, and the air quality goals described
therein. EPA appreciates that there has been substantial discussion
about the merits of the Submittals, including various opportunities for
public comment. Ultimately, however, when weighing alternatives, EPA's
final decision must be the one that is most consistent with the CAA,
even if that decision is reached through a reconsideration process. EPA
has already addressed its authority to review the October 15, 2008,
final action in response to comments above.
    Comment 9. Commenters asserted that in granting the second petition
for reconsideration and re-opening the rulemaking for further public
comment, EPA ignores the lack of a legal basis for reconsideration, its
earlier rejection of AEC's arguments for reconsideration on the merits,
and its thorough review and technical analysis of the effect of these
SIP revisions during the earlier rulemaking itself. According to the
commenters, reconsidering a SIP approval sets a poor precedent and
undermines regulatory certainty and the integrity of EPA's rulemaking
processes.
    Response 9. EPA does not agree with commenters' assessment. To the
contrary, the reconsideration process has ensured that EPA has left no
issue unconsidered in its analysis of the Submittals. EPA's final
action on the Submittals, while amended from its previous action, is
strongly grounded in the CAA, the APA, and sound science. This action
furthers the purposes of the CAA, is based on the substantive
requirements of the CAA, and follows the rulemaking requirements of the
CAA and the APA. Thus, the action supports regulatory certainty and the
integrity of SIP process. See, e.g. 73 FR 21528 (August 22, 2008) (EPA
reconsideration of Georgia SIP action). Indeed, the fact that the CAA
and the APA provide bases for reconsidering regulatory decisions
demonstrates that Congress expected EPA to take necessary action to
revise its actions when a party raises factual or legal issues that the
Agency finds justify reconsidering such actions.
    Comment 10. Commenters questioned why EPA granted the petition for
reconsideration of the approval of Alabama's Submittal because the
Petitioners have provided no new information.
    Response 10. As was discussed above, the APA does not restrict
EPA's authority to reconsider a rule to a specific record or timeframe.
EPA was petitioned for reconsideration of a rule and EPA granted that
reconsideration because it concluded that the petition raised factual
and legal issues that justified further evaluation. The second petition
for reconsideration raised numerous reasons why EPA's October 15, 2008,
final action should be reconsidered, including several reasons not
identified in the first petition for reconsideration. Thus, commenters'
characterization of the second petition for reconsideration as
providing no new information is also not correct.

2. Relationship Between Opacity and PM Emissions

    Comment 11. Commenters asserted that data submitted to EPA show
that there is no reliable or direct correlation between opacity and PM
emissions. In addition to several sources of uncertainty in the
relationship between changes in opacity and increases or decreases in
PM2.5 levels cited by EPA in the April 12, 2007, proposal
notice, the commenters argued that other variables affecting the
relationship of opacity and PM mass emissions include stack diameter,
stack gas temperature, particle density (a function of coal type), and
flue gas water vapor content. The commenters argued that many, if not
most, of these variables are beyond the control of source operators.
Therefore, the commenters stated that while opacity can serve as an
indicator of whether the boiler and related pollution control equipment
at a specific source are well-controlled and well-operated, changes to
opacity of emissions,

including changes to the SIP limits applicable to opacity in a SIP,
cannot be presumed to have any direct effect on ambient concentrations
of PM.
    Response 11. EPA generally agrees with commenters that there is
inherent uncertainty in the precise relationship between opacity and
ambient concentrations of PM, although we note that some variables are
less likely to vary during a single source's operation (as opposed to
among different sources). EPA also agrees (as a general matter) with
commenters' statements that opacity is useful as an indicator of a
source's operations and control technology. Moreover, opacity can be a
reliable indicator of PM emissions when appropriate source-specific
testing is carried out and correlations are established for the
particular source, operating characteristics, and fuel supply.
    EPA disagrees, therefore, that increases in opacity of emissions
per se could not reflect any increases in mass emissions under any
circumstances, in particular in the case of the significant increases
in the percentage opacity and the duration of excursion time at issue
in these SIP revisions. This comment highlights the importance of
ensuring that the final decision made by EPA to approve a SIP revision
is based on a reasoned application of that knowledge within the
confines of the CAA.
    Comment 12. Commenters argued that available data continue to
demonstrate there is no reliable, generally applicable relationship
between opacity and the PM NAAQS. The commenters asserted that previous
technical studies submitted by APC in the rulemaking confirm this lack
of correlation. The commenters referred to prior comments for the
assertion that: ``Because opacity is dependent on so many factors,
there is no general relationship between opacity and particulate
loading.''
    Response 12. EPA agrees that opacity data from different individual
sources are very specific to the source and to the manner in which it
is being operated for the period over which data is collected. In other
words, source operation affects data produced by the source. Thus, EPA
and others must consider not only the data on opacity and PM, but also
the details regarding the facility and its operating characteristics as
part of developing an opacity/PM correlation. As a result, such data
from one facility may be of limited value in extrapolating reliable
conclusions about emissions from another facility. However, EPA expects
that sufficiently high increases in opacity up to 100 percent for
extended periods can represent some impact on PM emissions from the
sources affected by the rules at issue in the Alabama SIP revisions. As
noted by comments received through the reconsideration process,
although the precise correlation between the mass and opacity of
emissions may vary, significant increases in opacity to its highest
measurable level at the same source are likely to result in additional
PM emissions from that source. Given that several sources are located
in and near nonattainment areas, such additional emissions are
inconsistent with the prohibition of section 110(l) on SIP revisions
that will interfere with attainment and maintenance of the NAAQS.
    Comment 13. One commenter asserted that EPA's prior conclusion that
greater opacity does not necessarily mean greater PM emissions is
entirely reasonable.
    Response 13. EPA appreciates commenters' position on this issue--
the uncertainty inherent in the relationship between opacity and PM is
discussed at length in this final action. While EPA agrees that greater
opacity does not necessarily (in all circumstances) mean greater PM
emissions, EPA does expect that some periods of greater opacity
(particularly of high opacity for longer periods of time) are likely in
at least some circumstances to be accompanied by greater PM emissions.
    Comment 14. A commenter agreed that it is difficult to accurately
characterize differences in direct PM2.5 emissions
attributable to short-term increases in opacity and further commented
that: (1) The type of event causing the short-term increase in opacity
will most probably have an effect on any direct PM2.5
emissions differences associated with the event, and (2) based on the
cumulative size distribution table in AP-42 (Compilation of Air
Pollutant Emission Factors), any increase in PM emissions associated
with short-term increases in opacity would most likely occur in
particle sizes larger than direct PM2.5.
    Response 14. Commenter appears to refer to Table 1-1.6,
``Cumulative Particle Size Distribution and Size-Specific Emission
Factors for Dry Bottom Boilers Burning Pulverized Bituminous and
Subbituminous,'' which is found in Chapter 1 of EPA's AP-42,
Compilation of Air Pollutant Emission Factors (http://www.epa.gov/ttn/chief/ap42/). This table suggests that for units having pollutant
emissions controlled by electrostatic precipitators (ESPs),
PM2.5 accounts for only 29 percent of total PM emissions.
EPA agrees the type of event causing an increase in opacity of
emissions may have an effect on the size distribution of PM emissions.
However, EPA disagrees that increases in PM emissions associated with
increases in opacity would most likely occur in particle sizes larger
than 2.5 micrometers in aerodynamic equivalent diameter, since the
circumstance that causes an opacity increase could occur while a PM
control device is operating properly, as described by the value
contained in the AP-42 table, or while a PM control device is not
operating properly, a condition not described in the AP-42 table. The
uncertainty regarding the impact of opacity increases on PM emissions
is further complicated because particles approximately 1.0 micrometer
in diameter have greater potential for increasing opacity than larger
particles. See, e.g., Malm, William C., ``Introduction to Visibility,''
Cooperative Institute for Research in the Atmosphere, May 1999 at Chap.
2, p. 8. Thus, for the increases in opacity contemplated in the SIP
revisions at issue in this rulemaking, EPA is concerned that this
increased opacity would probably include additional particles of the
very types that would be problematic for purposes of attaining and
maintaining the PM2.5 NAAQS.
    Comment 15. Commenters argued that with regard to EPA's request for
additional information addressing the relationship between opacity and
PM emissions generally, only the relationship between opacity and
direct PM2.5 would be relevant to the situation at hand, and
that this information would be virtually impossible to obtain due to
the inclusion of larger particles which are an inevitable part of any
effluent gas stream.
    Response 15. EPA agrees that information concerning the
relationship between opacity and PM2.5 emissions from a
facility would be most relevant for purposes of evaluating impacts on
the PM2.5 NAAQS, but EPA notes that no commenter provided
such data, despite EPA's specific request for such specific data. 74 FR
50934 (October 2, 2009). EPA disagrees that this information would be
virtually impossible to obtain. By way of example, some sources are
obtaining and reporting these data as part of the current electrical
utility maximum achievable control technology (MACT) rule information
collection request. Also, under section 110(l) of the CAA, EPA may not
approve revisions to SIP if the revisions would interfere with any
applicable requirement concerning attainment and reasonable further
progress (RFP), or any other applicable requirement of the CAA. Because
there are also NAAQS for PM10, states and EPA must also
consider potential

impacts of increases of larger particles if increased opacity were to
include the emissions of larger particles from a source as the
commenter asserted. For 110(l) purposes, analysis of a SIP revision
must include all of the current NAAQS, to the extent that the changes
in the SIP revision could affect such NAAQS. With respect to this
action, EPA has only focused on the potential impacts of the SIP
revision on the PM2.5 NAAQS because those are the standards
that EPA anticipates are most implicated by the increases in opacity at
issue.
    Comment 16. Commenters argued that although an increase in opacity
can be a good indication that PM emissions at the stack also are
increasing, the magnitude of mass emissions relative to any one opacity
value and the increase in mass emissions relative to increase in
opacity generally are not quantifiable. Accordingly commenters asserted
that an increase in opacity would provide no information regarding
emission levels of PM2.5, as opposed to PM10 or
total PM, and argued that any correlation between opacity and PM would
have to be source specific, and even then, uncertainties remain. The
commenters also criticized EPA's information on opacity and PM, noting
that the charts included in the docket do not contain sufficient
information to evaluate the relationship between opacity and PM.
    Response 16. EPA agrees that an increase in opacity can be a good
indication that PM emissions at the stack also are increasing. It is
for this reason that we are disapproving the SIP revision embodied in
the Submittals, even though the magnitude of mass emissions relative to
any one opacity value and the increase in mass emissions relative to
increase in opacity generally are not quantifiable. EPA also agrees
with the commenters that a correlation between mass and opacity can be
derived at a specific source, and EPA has in the past approved SIP
revisions that relied on such correlations with sufficient technical
analysis.
    EPA disagrees, however, that information about opacity increases
provides no information regarding PM2.5 emissions
specifically. Rather, information about opacity increases without
concurrent PM2.5 emissions data or an established
correlation between opacity and PM2.5 emissions cannot be
expected to yield definitive information concerning increases in
PM2.5 emissions. The memorandum in the docket, EPA-R04-OAR-
2005-AL-0002-0064, provides the information known to EPA about the
charts referenced by the commenter, EPA-R04-OAR-2005-AL-0002-0045 and
EPA-R04-OAR-2005-AL-0002-0047. Further, the charts provided in the
docket demonstrate the inherent uncertainty in the relationship between
opacity and filterable PM mass emissions by showing a range of mass
emission rates associated with a single opacity value and a range of
opacity values associated with a single mass emissions rate. However,
uncertainty about the precise correlation between mass and opacity as a
general matter, does not mean that opacity increases never represent
concurrent increases in the mass of PM emissions from a source. To the
contrary, given the large increases in maximum allowable opacity and
for the periods of time at issue in the SIP revision contemplated in
the Submittals, EPA expects that it is likely that there could be
increases in mass emissions.
    Comment 17. Commenter disputed the relationship between opacity and
PM mass emissions based upon EPA statements in an unrelated rulemaking.
The commenter asserted that despite providing the option for use of PM
continuous emissions monitoring system (CEMS) as a compliance method
for PM mass limits in revised NSPS Subparts D and Da, EPA also recently
suggested it had concerns regarding the accuracy of PM CEMS
measurements above 0.030 pounds per million British Thermal unit (lb/
mmBtu). As a result, the commenter argued that EPA declined to exempt
units operating above that level from the NSPS opacity standard even
when such sources install PM CEMS. 74 FR 5070 (January 28, 2009).
Commenter requested, to the extent EPA relies on data from PM CEMS
above 0.030 lb/mmBtu in this proceeding, that the Agency explain how it
resolved those concerns.
    Response 17. EPA disagrees with the commenter's conclusions
regarding PM CEMS measurement accuracy above 0.030 lbs/mmBtu. As
mentioned in the cited Federal Register notice, the contribution of
filterable PM to opacity at these emission levels (less than 0.030 lb/
mmBtu) is generally negligible, and sources with mass limits at this
level or less will operate with little or no visible emissions (i.e.,
less than 5 percent opacity). As a result, EPA expects that an opacity
standard is no longer necessary for such sources because the PM mass
emission rate standard is substantially tighter, and the use of PM CEMS
with continuous monitoring of PM emissions is more effective than
opacity monitoring in these circumstances.
    This comment is also not germane to today's action because the SIP
revisions at issue did not include the requirement that the affected
sources install PM CEMS as a precondition to the revision of the
applicable opacity standard. As noted above, opacity standards serve an
important role in assuring compliance with PM limits, for example by
alerting regulators to problems with source operation or control
measures that would not otherwise be noted except during a stack test
for PM emissions, which occur only periodically. In some circumstances,
opacity is the emission standard that is the subject of an enforcement
case.
    Comment 18. A commenter articulated the position that its
facilities are operating in compliance with PM limits in the title V
permits and as a result, the opacity rule is not likely to impact PM
compliance. The commenter further opined that ADEM should address any
PM nonattainment issues separately from this rulemaking.
    Response 18. EPA disagrees with the assessment that opacity is
unlikely to have any effect on PM emissions for all the reasons
explained in this final action regarding that relationship. Further,
Alabama's visible emissions rule is a part of Alabama's plan to attain
and maintain the PM NAAQS. Even though it has been in the SIP for some
time, the rule was originally included for that purpose. Thus there is
nothing separate about this action and Alabama's PM nonattainment
issues--the rule at issue here is part of Alabama's overall plan to
address the PM NAAQS. Further, if a source is in compliance with the
opacity and PM limits, then this disapproval action should have little
effect on that source.

3. Modeling

    Comment 19. Commenters argued that modeling is not required to
demonstrate that changes to Alabama's opacity rule will not implicate
the NAAQS. Nonetheless, commenters argued that ADEM performed a
modeling analysis demonstrating that even earlier versions of the SIP
revision (predating the Submittals that EPA approved in October 2008)
would not adversely affect air quality attainment or RFP under very
conservative assumptions about the relationship between opacity and PM
emissions. In addition, commenters argued that updated modeling from a
consultant, ENSR (now known as AECOM), updated ADEM's 2003 modeling in
2007 using AERMOD (an atmospheric dispersion modeling system and EPA's
preferred model since 2005) and confirmed ADEM's earlier modeling
results. Commenters argued that APC and TVA have performed subsequent
modeling that also

supported the conclusion that the increased opacity permitted by the
SIP revisions in the Submittals would not interfere with attainment and
maintenance of the NAAQS or other requirement of the CAA. Commenters
asserted that these modeling results show no problem with the NAAQS
even under unrealistic, worst-case conditions. APC also discussed
modeling done at APC Plants Barry and Greene and TVA Plant Colbert
which APC believes supports affirming EPA's 2008 final action approving
the Alabama SIP revisions. Commenters further noted that ADEM performed
a modeling analysis demonstrating that the SIP revisions would not
affect air quality attainment under very conservative assumptions about
a relationship between opacity and PM emissions. According to the
commenters, modeling performed by TVA confirms that particulate
emissions from the Colbert facility would not interfere with
maintenance of the PM10 or PM2.5 NAAQS, even for
the unrealistic scenario in which the ESPs are shut down for 10 percent
of the time every day of the year.
    Response 19. EPA disagrees with the commenter's assertions. As
discussed in 73 FR 60961 (October 15, 2008), all modeling results are
predicated on a known or assumed correlation between opacity and PM
mass emissions. Because this correlation can differ for each source and
operating condition, modeling that does not use source-specific
correlations does not and cannot demonstrate with certainty the impact
of changes in opacity on PM NAAQS. With respect to the modeling
described by the commenters, the models do not demonstrate that the
Submittals would not interfere with attainment or maintenance of the
NAAQS because the models do not appear to have included condensable PM
or background analyses, to have assessed the impact of nearby PM
emissions sources, or to have assessed the impact of secondary PM
formation. Generally, however, the utility of modeling would still be
limited because the precise relationship between opacity levels and PM
mass emissions is not known. The docket for this action includes a
technical support document (TSD) summarizing the modeling that EPA
received and some of the key assumptions and other issues that impacted
the utility of the modeling.
    Comment 20. Commenters argued that EPA has routinely approved SIP
demonstrations based on the use of air models, rightly concluding in
such matters that the use of the air models leads to a reasonable
demonstration of compliance with the NAAQS.
    Response 20. As a general matter, EPA agrees that modeling can be a
useful tool in appropriate circumstances. In this case, the modeling
provided did not reduce uncertainty regarding the relationship between
opacity and PM emissions sufficiently to support approval of the
Submittals. Further, the modeling did not conclusively demonstrate that
there would be no impact on the NAAQS. Thus, EPA could not conclude
that the modeling submitted supported approval of the Submittals under
section 110(l). EPA's modeling TSD provides more information on the
modeling submitted to EPA as part of this action.
    Comment 21. Commenters stated that monitoring data show a decline
in ambient PM2.5 and PM10 levels at monitors that
could potentially be impacted by TVA's Colbert and Widows Creek Plants.
    Response 21. EPA acknowledges that ambient PM levels have been
improving in many parts of the country as a result of rigorous state
and EPA efforts to control emissions from many sources of various
types. EPA wants to maintain these improvements and to support further
improvements for protection of public health as many areas are still
designated nonattainment for the NAAQS. Indeed, this is among the
reasons why reviewing SIP revisions pursuant to section 110(l) is such
an important exercise.

4. Relative Stringency of Previous Rule (Pre-2008 Final Action) to
Current Rule (Post 2008 Final Action)

    Comment 22. Commenters argued that Petitioners' claims regarding
``bundling'' or other potential ways of ``using'' Alabama's visible
emissions revisions to somehow reduce control efforts while still
meeting permit requirements are misplaced. According to the commenters,
it is extremely difficult to achieve continuous or near-continuous
compliance with the opacity rules, so there is absolutely no incentive
to try to ``game'' the system by trying to achieve less than maximum
opacity control at any one time. Further, commenters argued that
facility procedures aimed at minimizing opacity levels at all times in
order to avoid non-exempted exceedances insofar as practicable remain
intact after the rule revisions went into effect January 1, 2009.
    Response 22. The commenters' argument appears to be that even
though ``bundling'' could occur, it will not, because sources are
diligently striving to minimize their opacity levels. While EPA
certainly expects that sources are seeking to minimize their opacity
levels, EPA's analysis of the revision considered what the two versions
of the Alabama rules allowed--and not necessarily how sources were
operating under each rule scenario. As with the modeling submitted by
many commenters, the primary problem associated with their conclusions
about the amount of PM emissions during longer periods of elevated
opacity is the reliance on an assumed relationship between opacity and
PM emissions that has not been established for the specific source. As
mentioned previously, this relationship is unknown for each source and
operating condition, absent sufficient evaluation. EPA disagrees that
the ``bundling'' of periods of high opacity could never reflect higher
PM mass emissions.
    EPA understands the difficulties associated with operating older
facilities, but disagrees that continuous compliance with opacity rules
can be achieved only through extreme difficulty. The Alabama SIP
opacity limits in effect following this disapproval should generally be
capable of being met by a source that is properly maintained, operated
and controlled. There are control technologies and operational
paradigms that allow older facilities to comply with Alabama's pre-
October 15, 2008, opacity rules (this was recognized by the court in
the TVA Colbert case, Sierra Club v. TVA, 592 F. Supp. 2d 1357 (N.D.
Ala. 2009)).
    Comment 23. Commenter explained that to attempt to bundle six-
minute opacity exceedances would necessitate a purposeful ``turn-down''
of the unit's ESP and, thus, result in non-compliance with two
provisions of the commenter's Lowman Plant's major source operating
permit (title V permit): (1) That ``all air pollution control devices *
* * be * * * operated at all times in a manner so as to minimize the
emissions of air contaminants,'' and (2) once the emissions exceed a
six-minute average opacity of 20 percent, corrective actions must be
taken within two hours.
    Response 23. EPA's analysis of the SIP revisions at issue is
governed by, among other provisions, section 110(l) of the CAA. In that
context, as was explained previously, EPA must compare the existing SIP
and the proposed SIP revision. While affected sources may have permit
limits that are more stringent than the applicable SIP regulations,
EPA's analysis must focus on what the SIP itself would allow. Permits
may be revised from time to time, depending on applicable requirements.
As a result, the type of analysis completed by the commenter based on
the applicable permits might

be changed over time. Further, while EPA would, of course, be concerned
by a purposeful ``turn-down'' of any control device, EPA expects that
there are other circumstances under which extended periods of
consecutive exemptions would allow high opacity levels (and mass
emissions) that would not occur in a well-operated, well-controlled,
and well-maintained plant. EPA appreciates PowerSouth Energy
Cooperative's (PSEC's) analysis, which demonstrates that this
disapproval action should have little effect on the vast majority of
sources.
    Comment 24. Commenters provided data in three attachments provided
by PSEC showing emissions during the period of January 1, 2009, thru
September 30, 2009, clearly indicate that no ``bundling'' occurred. For
example, Attachment 1 shows that of the total of 90 six-minute periods
of excess opacity (i.e., six-minute averages of opacity greater than 20
percent), including startup/shutdown and load change periods, there
were 40 occurrences of isolated six-minute periods of excess opacity;
14 occurrences of two consecutive six-minute periods of excess opacity;
four occurrences of three consecutive six-minute periods of excess
opacity; one occurrence of four consecutive six-minute periods of
excess opacity; and one occurrence of six consecutive six-minute
periods of excess opacity.
    Response 24. EPA appreciates the submission of operating data. One
of the difficulties with the technical analysis regarding opacity is
that details regarding facility operation can impact both opacity and
PM in different ways. Further, EPA must consider the effect of the
Submittals on how a facility may be allowed to operate, not just how
the facility actually has been operating. With these considerations in
mind, the operating data were informative, but not determinative,
because even if a facility currently operates as the commenters
describe, the facility would be allowed to operate otherwise under
Alabama's proposed SIP revisions.
    Comment 25. Commenters suggested that this 22 percent limit ensures
that the average daily opacity under the revised SIP is no greater than
under the previous SIP. The commenters asserted that this fully
responds to AEC's hypothesis of the ``bundling of high opacity
periods'' and concerns about the elimination of the ``40 percent cap''
under the revised SIP. Further the commenters explained the use of a
daily opacity limit to establish short-term equivalency is appropriate
because a calendar day is the shortest period over which compliance
with the PM NAAQS is measured. The commenters stated that AEC provides
no supporting data on the bundling and operating data provided, which
commenters believe demonstrates that bundling has not occurred.
    Response 25. The Commenters' statements are incomplete. While the
22 percent limit does serve the purpose of ensuring subject sources are
constrained by the same maximum allowable average daily opacity as
under the previously approved SIP (as explained in EPA's 2008 final
notice), these SIP revisions would allow opacity levels of up to 100
percent during exempt periods and for multiple consecutive exempt
periods, neither of which was previously authorized under the SIP. The
prior version of the visible emissions rule capped maximum opacity at
40 percent and limited the time at such level to only six minutes per
hour. Further, whether ``bundling'' in fact has occurred in the past is
not the focus of EPA's analysis for purposes of section 110(l).\20\ As
part of this reconsideration, EPA has had to re-evaluate the concept of
the ``22 percent daily cap'' supported by the commenter. EPA has
concluded that even with an ``average daily opacity'' cap, these SIP
revisions undermine the purpose and effectiveness of the opacity
standard by allowing extended periods of high opacity. Such high
opacity can be indicative of problems with control device operation or
other circumstances potentially leading to increased mass emissions.
Given that some sources affected by the opacity limits at issue in the
SIP revisions are located within designated nonattainment areas, EPA
concludes that this likelihood of increased emissions renders the
Submittals unapprovable under section 110(l).
---------------------------------------------------------------------------

    \20\ The SIP revisions at issue have been under reconsideration
since before the changes to Alabama's visible emissions rule now
being disapproved went into effect; thus, the data submitted in
public comments may not be a representative random sampling of the
long-term effects of the rule.
---------------------------------------------------------------------------

    Comment 26. Commenters argued that the equivalency between the
previous and revised SIPs, with respect to the short-term and long-term
emission rates, will ensure that there will be no interference with
NAAQS notwithstanding the bundling of high opacity periods. Further,
the commenters mentioned that in approving the North Carolina SIP
revision for visible emissions, EPA concluded that such bundling
through the ``elimination of the current restriction of no more than
one six minute exception period per hour'' does not ``pose a problem
for purposes of Section 110(l).'' Commenters cite to 70 FR at 61558 for
support.
    Response 26. As EPA explained earlier in this final action, the
North Carolina opacity revisions are not analogous to Alabama's opacity
revisions for the main reason that Alabama's revisions allow for
periods of opacity up to 100 percent, whereas the North Carolina
revision retained the same maximum opacity of 40 percent. The allowance
for this high opacity level, along with the lengthy time allowed for
elevated opacity (up to 2.4 consecutive hours), was not present in the
North Carolina case.
    Comment 27. Commenters argued that plant operating data confirm
that the bundling of high opacity periods does not occur in practice.
Further, the 22 percent cap resolves any concerns regarding the
bundling were it to occur.
    Response 27. EPA appreciates commenters' information on actual
operations; however, as explained previously EPA's analysis under
section 110(l) focuses on what the revised SIP rules would allow.
Further, as discussed above, the 22 percent cap does not resolve EPA's
concerns about extended periods of very high opacity.
    Comment 28. Commenters argued that the rule really has nothing to
do with air quality, and that if it did, EPA would have to justify and
explain why it is proposing to condemn an opacity rule that is
numerically more stringent and that has fewer exemptions than many
other states' opacity rules.
    Response 28. EPA does not agree with commenters' statements.
Alabama's visible emissions rule is part of Alabama's EPA-approved SIP,
and part of its plan to attain and maintain the PM NAAQS. As a result,
any revision of the EPA-approved opacity rules is subject to evaluation
under section 110(l) of the CAA. Furthermore, the extended consecutive
periods of opacity exemptions allowed renders this standard uniquely
less stringent than any other EPA-approved opacity rule.
    Comment 29. Commenters argued that the daily opacity limit is
neither necessary for approval nor unlawful. According to the
commenters, because EPA's proposed approval was not based on a finding
that the rule would not allow any more PM during a 24-hour period than
the old rule, it is not necessary for the daily limit to meet such a
criterion.
    Response 29. EPA disagrees that the potential for more PM emissions
as a result of elevated opacity is not germane to this action. EPA's
prior approval of the SIP revisions was based on uncertainty about
whether the revisions

to the opacity standard would allow more PM emissions during a 24-hour
period. EPA would not have previously proposed approval if the record
clearly demonstrated that the rule would have resulted in increased PM
in nonattainment areas. After reviewing public comment and the State's
revised submissions, EPA based its prior approval in part on the
average daily opacity limit included in the revision. At that time, EPA
accepted certain assumptions, including that the 22 percent daily
opacity limit would serve to lessen the potential for elevated
emissions of PM associated with the increases in opacity. Following
EPA's reconsideration and review of information submitted to EPA, EPA
no longer accepts that the average daily opacity limit is an
appropriate or effective tool for evaluating the impact of the
Submittals on PM emissions. Given EPA's position that there is a
sufficient likelihood of increased PM emissions associated with the
elevated opacity allowed under the SIP revisions, the Submittals are
not approvable under 110(l).

5. Attainment and Maintenance of the PM NAAQS (PM10 and
PM2.5) and Data Submitted in Response to October 2009
Reconsideration Proposal

    Comment 30. Commenter argued that while the Clean Air Fine Particle
Implementation Rule requires that direct PM2.5 emissions be
addressed in PM2.5 attainment demonstration SIPs, the
primary thrust of the regulation is the control of precursor compounds
and not direct PM2.5 emissions. According to the commenters,
if the Alabama attainment plans are similar to those of Tennessee in
that sulfates are identified as the main contributor to fine
particulate matter and reliance is being placed on reductions of sulfur
dioxide (SO2) to demonstrate compliance, with no measure
specified for stationary direct PM2.5, then the Petitioners'
assertion that approval of the Alabama SIP revisions would adversely
affect PM2.5 attainment or RFP has no merit and should be
rejected. The commenters explained that if this is the case then the
Petitioner's assertion that approval of the Alabama SIP revisions would
not be consistent with sections 110(l) and 193 of the CAA should also
be rejected as having no merit unless it can be demonstrated that a
fixed source of direct PM2.5 is a significant contributor to
a nonattainment area. Additionally, according to the commenters, this
should be an adequate affirmative demonstration that the requirements
of sections 110(l) and 193 of the Act are not an issue. Further, the
commenters asserted that even for areas achieving conformance with the
PM2.5 ambient standard, for which no SIP would be required,
the effect of the reductions of PM2.5 precursors would be so
dominant as to negate any changes to direct PM2.5 emissions.
    Response 30. As was explained earlier, given that ADEM did not
submit a full attainment demonstration specifically addressing this
rule and did not propose any offsetting reductions to compensate for
emission increases in nonattainment areas, EPA's analysis is
necessarily focused on the comparison between the previous EPA-approved
version of the visible emissions rules and the revisions that the State
seeks, in order to ensure that the revision would not allow an increase
in emissions of pollutants that would interfere with attainment or
maintenance of the NAAQS, or with other requirements of the CAA. A
primary consideration, therefore, is whether the revisions could result
in increases in emissions of a type for which the area where the source
is located is designated nonattainment. In this context, EPA must
evaluate the relative stringencies of the two versions of the opacity
rules, as was explained earlier.
    EPA notes that the commenter's arguments here are premised upon
what might or might not be appropriate in the context of a
nonattainment SIP for certain pollutants in an area. EPA does not agree
that the implementation regulations for the 1997 PM2.5 NAAQS
are designed or intended to ignore direct PM2.5 emissions
from sources, and evaluation of controls for such emissions is a
required element of such a SIP. While it may be correct that a
nonattainment SIP in a particular area might be designed to focus upon
emissions of SO2 and nitrogen oxides, or other
PM2.5 precursors, as an attainment strategy, it does not
follow that emissions of PM2.5 from the sources subject to
Alabama opacity rule do not impact attainment and maintenance of these
NAAQS. Considerations mentioned by the commenters might be relevant in
the evaluation of the attainment demonstration accompanying a
nonattainment SIP for the 1997 PM2.5 NAAQS, but they are not
relevant in the context of a section 110(l) analysis.
    Comment 31. Commenters argued that Alabama's revised SIP for
visible emissions is a small piece in the overall PM attainment puzzle.
According to the commenter, any incremental primary PM2.5
emissions increase as a result of revising the SIP, assuming for
purposes of argument that such an increase occurs, would be an
inconsequential contributor to the PM2.5 attainment status
against the background of the significantly greater secondary
PM2.5 (sulfate and nitrate) contributions. The commenter
asserted that viewed in this broader context, EPA could reasonably
conclude, based on the equivalency demonstration, that the revised SIP
is consistent with the earlier SIP.
    Response 31. The comment fails to appreciate EPA's limitations in
reviewing SIP revisions, as described in section 110(l). In addition,
EPA did not receive an ``equivalency demonstration'' from ADEM that
addressed all the elements in section 110(l). Further, an increase of
PM emissions by any increment would make it more difficult for areas in
Alabama to attain and maintain the NAAQS. EPA has considered the SIP as
a whole, and concludes that the potential increase renders the
revisions not approvable.
    Comment 32. Commenters explained that following new data collected
under the current SIP confirms that EPA's prior analysis was sound:
    A. New data collected under the current SIP shows there is no
``bundling;''
    B. New data collected under the current SIP shows that daily
opacity has improved; and
    C. New data collected under the current SIP shows why the rule
makes sense.
    Response 32. EPA appreciates the submission of these data. EPA
disagrees, however, with the conclusions that the commenters draw from
the data. The commenters' focus on what is actually happening with
respect to ``bundling'' and opacity levels fails to consider what could
happen under the SIP revision. EPA's analysis pursuant to section
110(l) must focus on the differences between the two versions of the
visible emissions rules in terms of what they would allow and not on
the choices individual facilities may have made to date in terms of
opacity and PM emissions. Thus, EPA does not agree that the data
presented by commenters support approval of the Submittals. The
commenters did not, unfortunately, submit data to establish what the PM
mass emissions were during periods of elevated opacity at these
sources.
    Comment 33. Commenter saw no basis for the supposition that
Alabama's opacity rule revisions will affect PM NAAQS compliance. The
commenters asserted that as indicated in the attachments, PSEC's Lowman
Unit 1's opacity compliance continues to be very good. Additionally,
the commenters explained that annual particulate emission testing in
2008 and 2009 indicate PM emissions well below the

standard and show no difference before and after the opacity rule
revisions.
    Response 33. EPA acknowledges that some facilities affected by the
SIP revisions may be operating at opacity levels below those required
by the Alabama SIP. Indeed, a source that is well-controlled, well-
maintained, and well-operated could achieve opacity levels well below
20 percent. However, EPA's obligation under section 110(l) is to
consider how a facility could operate under the new rule--not how it
typically operates or has historically operated. Moreover, EPA notes
that annual PM testing offers valuable but limited information about
mass emissions because the testing occurs only once per year for a
limited period of time. The question not addressed by the comments is
what the PM mass emissions would be, were a source to be operating at
the 100 percent opacity for 2.4 hours contemplated by the SIP revision
at issue.
    Comment 34. Commenters asserted that there are no new data that
would support EPA's withdrawal of its approval of the rule.
    Response 34. As was discussed previously, EPA's authority to
reconsider a SIP revision is not limited only to circumstances where
there are new data. EPA has already explained in today's action why its
prior approval was not consistent with the purposes of section 110(l),
and that reconsideration and disapproval is appropriate. Notably, the
reconsideration was initiated before the revised rule went into effect
and that sources should be capable of complying with either rule or
both rules simultaneously.
    In addition, EPA disagrees that no new information supports this
disapproval. A number of commenters have submitted data and information
that, while not directly addressing the questions that EPA posed,
nevertheless help to illustrate the problems with the SIP revisions.
For example, information submitted by AEC suggests that at least some
sources, under some conditions, could have increased PM emissions
during the longer periods of higher opacity that would be permissible
under the revised visible emissions rules in the Submittals. See
Comment Letter from George E. Hays and attachments (on behalf of
Alabama Environmental Council, among others), Docket No. EPA-R04-OAR-
2005-AL-0002-0089.1. Moreover, many of the commenters during the
reconsideration process submitted comments in which their analysis
suggested that there is a relationship between PM mass emissions and
opacity, even if the precise correlation cannot be established without
much more rigorous testing and evaluations on a source specific basis.
See Modeling TSD. As was noted earlier, even some of the commenters
opposing EPA's disapproval action identified the uncertainty in the
relationship between opacity and PM mass emissions, and the possibility
of the SIP revisions resulting in emission increases. See, e.g.,
Comment Letter from Lauren E. Freeman (on behalf of the Utility Air
Regulatory Group) at 4, Docket No. EPA-R04-OAR-2005-AL-0002-0086.1.
    Comment 35. Commenter noted that with regard to EPA's request for
information on condensable PM, COMS do not measure condensable PM,
which is in a gaseous form at stack conditions.
    Response 35. EPA acknowledges the response, which underscores one
component of the uncertainty inherent in the relationship between
opacity and PM emissions.

6. Impact of Uncertainty in These SIP Revisions

    Comment 36. Commenters asserted that while EPA has consistently
(and correctly) noted the uncertain relationship between opacity and PM
for short-term analysis, any question regarding how this uncertainty
might impact PM, in this case, has now been eliminated entirely with
the addition of the 22 percent daily average requirement. Commenters
further stated that ADEM's August 2008 submittal remedied any
``uncertainty'' question with respect to 24-hour PM by including an
additional restriction on daily average opacity, so that the average
daily opacity allowed under the revision is now no greater than under
the previous SIP.
    Response 36. EPA has shown through calculations, that the maximum
allowable average daily opacity under both the previous rule and the
revised rule is 22 percent. However, as discussed above, the revised
visible emissions rule at issue in the SIP revisions would allow
sources to operate in a manner they could not under the previous rule--
including increases in opacity concentrations up to 100 percent for an
extended period of time. As a result, under the revised rule, sources
may now be permitted to cause much more opacity to levels that would
have been a violation under the previous EPA-approved SIP rules. Such
emissions include very high concentrations of excess opacity for
extended periods. EPA has thus concluded that the ``average daily
opacity'' cap provides no assurance against increased mass emissions.
Indeed, as discussed above, EPA has concluded that there is a
sufficient likelihood of increased mass emissions under the revisions
so as to make it unapprovable under section 110(l).
    Comment 37. Commenters stated that there is always some uncertainty
when attainment or interference with a NAAQS is considered in a SIP
process because it involves an element of prediction and reliance on
modeling. Further, commenters explain their positions that section
110(l) does not require absolute certainty and EPA should not
substitute ``could'' for ``would'' in the 110(l) context.
    Response 37. EPA agrees the Act does not require attainment
demonstrations or other technical analysis of impacts on attainment or
maintenance of the NAAQS to an ``absolute certainty.'' However, to make
a determination that the NAAQS will not be adversely impacted, EPA must
at least be able to reach the conclusion that this is most likely the
case. In this action, EPA is relying on what is known about the
relationship between opacity and PM emissions to conclude that the
State's revised visible emissions rules in the Submittals is less
stringent than the previous EPA-approved rule, and that the likely
increases in emissions of PM at affected sources would be inconsistent
with section 110(l). Under the revised rule, a source could exceed its
20 percent opacity limit for well over an hour (up to 100 percent
opacity). In contrast, the previous SIP-approved rule allowed only one
occurrence per hour of a 6-minute average opacity above 20 percent (and
only up to 40 percent). Control equipment that is effective enough to
avoid a second occurrence of 6-minute average opacity above 20 percent
will make even the first occurrence an infrequent event. Likewise,
control equipment and operating procedures that are effective enough to
enable a unit to meet the requirements of the previous SIP will also
allow a lesser quantity of PM emissions than control equipment and
operating procedures that are sufficient to comply with the current SIP
revision but do not necessarily enable a unit to comply with the
previous SIP rule.
    In addition, contrary to the commenters' belief, this is not
dependent upon replacing the word ``would'' with the word ``could.''
EPA's conclusion is that available evidence indicates that some of the
affected sources would have increases in PM emissions, and that these
emissions would occur in locations where such increased emissions would
interfere with attainment and maintenance of the NAAQS. Commenters
evidently misconstrue ``uncertainty'' about the

precise amount of such likely emissions increases as evidence that no
such increases could occur.
    Comment 38. Commenters raised concerns regarding PM CEMS
technology, and the representativeness of PM emissions data obtained
during Performance Specification (PS) 11 testing. See 40 CFR part 60,
Appx. B. Briefly, the commenters asserted that PS 11 correlation
testing, which requires disabling of PM control devices under
artificial conditions in order to obtain sufficient variability in PM
emissions to satisfy the PS 11 statistical criteria, rarely provide
data representative of actual operations or control device
malfunctions. Commenters also noted that it would not make sense to
require sources to spend money to install PM CEMS or to perform
periodic performance tests in order to develop a source-specific
correlation between opacity and PM.
    Response 38. EPA disagrees with the commenter's views regarding PM
CEMS technology and PS 11 testing, especially in the context of
evaluating the SIP revisions at issue here. The procedures of PS 11 are
conducted to develop a source-specific PM emissions correlation for an
individual source operating over a range of PM emissions conditions
through comparison of results from PM emissions testing and PM CEMS.
Note that PS-11 does not require PM control devices to be disabled.
Those PM measurement and testing correlation procedures differ from an
opacity and PM emissions correlation, which is the fundamental issue
requiring resolution for addressing the visible emissions rules
revision in Alabama's Submittals. EPA also disagrees that use of PM
CEMS or periodic performance testing could be ``nonsensical'' in
determining a source-specific correlation between opacity and PM
emissions. Indeed, as EPA has previously explained, source-specific
approaches such as concurrent opacity and PM emissions measurements may
be one way to determine ``* * * any useful and definitive relationships
between stack particulate mass emissions values and their corresponding
opacity levels * * *'' 73 FR 60962 (October 15, 2008).
    EPA agrees that data obtained over a range of operating and control
device conditions would be necessary to develop a site-specific
correlation between opacity and PM emissions and that a single, site-
specific correlation should not be extrapolated to other sources.
Retaining Alabama's original visible emissions rule (the pre-October
15, 2008, final rule) relieves ADEM (and affected sources) from
performing an assessment of increased source opacity on PM emissions.
    Comment 39. Commenters suggested that the source-specific nature of
the opacity/PM relationship does not mean that the uncertain impact of
a particular change in an opacity rule can be resolved by requiring
source-specific testing.
    Response 39. EPA agrees that a well-designed data collection
program should be able to reduce to acceptable levels, if not
eliminate, most of the uncertainty associated with the relationship
between PM emissions and opacity resulting from changing opacity
limits. However, as the commenters themselves argue, the variability in
the relationship between PM emissions and opacity limits is such that,
absent the use of PM CEMS, source specific evaluation would be one way
to determine the impacts of the change at a given source. EPA through
this disapproval is not determining that the only means to revise an
opacity standard is through source by source evaluation, nor is EPA
requiring that with today's action.
    Comment 40. Commenters argued that to the extent that EPA seeks
information on PM compliance methods in order to assess the costs of
requiring Alabama to impose more source-specific PM testing in order to
evaluate the impact of its revised opacity rule, commenters disagree
that such an evaluation is required under CAA 110(l).
    Response 40. EPA agrees that an assessment of the cost of a
potential requirement for source-specific testing is not necessary
pursuant to section 110(l). In order to fully provide the public with
an opportunity to comment on the proposed action, EPA sought specific
information, including costs, to assist the public in identifying what