Document ID: EPA-R04-OAR-2005-AL-0002-0006
Agency: epa
Document Type: Proposed Rule
Title: Approval and Promulgation of Implementation Plans: Alabama: Proposed Approval of Revisions to the Visible Emissions Rule
Posted Date: 2007-04-12T04:00Z

[Federal Register: April 12, 2007 (Volume 72, Number 70)]
[Proposed Rules]               
[Page 18428-18434]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr12ap07-31]                         

[[Page 18428]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R04-OAR-2005-AL-0002-200623; FRL-8298-1]

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

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to approve the Visible Emissions portion of 
the State Implementation Plan (SIP) revision submitted to EPA, by the 
Alabama Department of Environmental Management (ADEM), on September 11, 
2003 (the ``2003 ADEM submittal''), provided it is revised as described 
in this action and submitted as a SIP revision. The open burning 
portion of the submittal was previously approved in a separate action 
on March 9, 2006 (71 FR 12138).

DATES: Comments must be received on or before June 11, 2007.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R04-
OAR-2005-AL-0002, by one of the following methods:
    (a) http://www.regulations.gov: Follow the on-line instructions for 

submitting comments.
    (b) E-mail: harder.stacy@epa.gov.
    (c) Fax: 404-562-9019.
    (d) Mail: ``EPA-R04-OAR-2005-AL-0002,'' 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.
    (e) Hand Delivery or Courier: Stacy Harder, Regulatory Development 
Section, Air Planning Branch, Air, Pesticides and Toxics Management 
Division, 12th floor, U.S. Environmental Protection Agency, Region 4, 
61 Forsyth Street, SW., Atlanta, Georgia 30303-8960. Such deliveries 
are only accepted during the Regional Office's normal hours of 
operation. The Regional Office's official hours of business are Monday 
through Friday, 8:30 to 4:30, excluding federal holidays.
    Instructions: Direct your comments to Docket ID No. ``EPA-R04-OAR-
2005-AL-0002.'' EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
online at http://www.regulations.gov, including any personal 

information provided, unless the comment includes information claimed 
to be Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. Do not submit through 
http://www.regulations.gov or e-mail, information that you consider to be CBI 

or otherwise protected. The http://www.regulations.gov Web site is an 

``anonymous access'' system, which means EPA will not know your 
identity or contact information unless you provide it in the body of 
your comment. If you send an e-mail comment directly to EPA without 
going through http://www.regulations.gov, your e-mail address will be 

automatically captured and included as part of the comment that is 
placed in the public docket and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses. For additional information about EPA's public 
docket visit the EPA Docket Center homepage at http://www.epa.gov/epahome/dockets.htm
.

    Docket: All documents in the electronic docket are listed in the 
http://www.regulations.gov index. Although listed in the index, some 

information is not publicly available, i.e., 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 in 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 
legal holidays.

FOR FURTHER INFORMATION CONTACT: Stacy Harder, 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. The telephone number is (404) 
562-9042. Ms. Harder can also be reached via electronic mail at 
harder.stacy@epa.gov.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. What Action Is EPA Proposing?
II. Why Is EPA Proposing This Action?
III. What Is the Rationale for This SIP Revision?
IV. What Does the Visible Emissions Rule in the Current SIP Require, 
and What Changes Are Requested by ADEM?
V. What Changes Does EPA Recommend to the Submittal?
VI. What Technical Analysis Was Used To Support Approval of This SIP 
Revision?
VII. What Happens Next?
VIII. Proposed Action
IX. Statutory and Executive Order Reviews

I. What Action Is EPA Proposing?

    EPA is proposing an approval, under Section 110(k) of the Clean Air 
Act (CAA), of the Visible Emissions portion of the Alabama SIP revision 
submitted on September 11, 2003. This proposed approval is contingent 
upon Alabama submitting a revised SIP submission addressing EPA's 
concerns regarding impacts of the rule changes on attainment of the 
National Ambient Air Quality Standards (NAAQS). Because the necessary 
revisions would materially alter both the existing SIP approved rule 
and the submitted revision, the State must make a SIP submittal to 
effect the changes noted by EPA below. As with any SIP revision, the 
State must provide public notice of and a public hearing on the 
proposed changes. If, after consideration of public comments, EPA 
determines the revised SIP submission meets the requirements of the CAA 
and is consistent with the recommended changes outlined in this action, 
the Agency may proceed to publish its approval of the revised SIP in 
the Federal Register. Alabama's revised submittal must be consistent 
with the changes discussed in this action for EPA to approve its 
incorporation into the SIP. If the revised language does not conform 
specifically to the recommended changes, EPA will need to re-evaluate 
Alabama's submittal and, if the changes are approvable, re-propose 
approval of the SIP submittal.

II. Why Is EPA Proposing This Action?

    EPA is taking this action in response to a request from ADEM to 
revise the Visible Emissions portion of Alabama's SIP rule pertaining 
to sources of particulate matter (PM) emissions. The request, submitted 
to EPA on September 11, 2003, would revise Alabama SIP rule 335-3-4-.01 
(``Visible Emissions'') by amending the requirements for units

[[Page 18429]]

that operate continuous opacity monitoring systems (COMS) and that are 
not subject to any opacity limits other than those in rule 335-3-
4-.01(1) (``Visible Emissions Restrictions for Stationary Sources'').
    Under section 110(l) of the CAA, EPA may not approve revisions to 
SIPs if the revisions would interfere with any applicable requirement 
concerning attainment and reasonable further progress (RFP), or any 
other applicable requirement of the CAA. In determining whether to 
approve a requested revision, EPA considers the relevant impacts of the 
proposed change in light of the type of requirement affected by the 
requested revision. In this instance, the State is proposing revisions 
to its opacity requirements. We define opacity as the degree to which 
emissions reduce the transmission of light and obscure the view of an 
object in the background. (See 40 CFR 60.2).
    A change in opacity standards may not necessarily impact on a 
State's ability to meet the PM NAAQS or any other applicable 
requirement of the Act because, as discussed further in this action, a 
reliable and direct correlation between opacity and PM emissions cannot 
be established without significant site-specific simultaneous testing 
of both PM emissions and opacity, particularly for short-term periods 
(e.g., 24 hours or less). Nonetheless, because there is at least an 
indirect relationship between opacity and PM emissions, including the 
use of opacity to track the effectiveness of PM control equipment 
operation, we considered the impact of Alabama's proposed revision on 
the NAAQS for PM10 and PM2.5, and on other applicable requirements. No 
changes are being proposed to revise the particulate mass limits in the 
Alabama SIP, and sources must continue to meet applicable emissions 
limits. EPA proposes to approve Alabama's revision, with our 
recommended changes, because we determined that, with the changes 
specified in this action, the SIP revision will not interfere with 
attainment of either of the PM NAAQS or with other applicable 
requirements.

III. What Is the Rationale for This SIP Revision?

    Monitoring opacity by use of COMS provides far more data than EPA 
Reference Method 9, the compliance determination method specified by 
most SIPs, including Alabama's. Alabama adopted into the State's 
regulations the rule revision contained in the 2003 ADEM submittal on 
August 26, 2003, and has since operated under it as a State-only 
enforceable provision. The purpose of that rule revision was to make 
the State's regulation consistent with what had been its practice in 
exercising enforcement discretion with respect to use of COMS data 
since the early 1980's.
    In addition to requiring corrective actions and prompt reporting of 
deviations from permit terms, the State has other oversight procedures 
in place that ensure long, continuous periods of high opacity are 
properly addressed by the source. ADEM receives quarterly emissions 
reports from plants that utilize COMS, which indicate the opacity of 
the emissions from sources subject to this rule revision. ADEM reviews 
the information and determines if further action should be taken due to 
any opacity exceedances. The data is required to be in a format that 
includes source operating time, monitor operating time, exempt opacity 
exceedances, and non-exempt opacity exceedances. The reports include 
daily opacity exceedances as well as a summary of the data for the 
entire quarter. In these reports, the sources also calculate the 
percentage of operating time in which they had non-exempt opacity 
exceedances as well as the percentage of operating time with any (total 
of exempt and non-exempt) opacity exceedances.
    ADEM has developed a program that takes the summary data from the 
quarterly opacity reports and calculates the percentage of source 
operating time that the opacity of emissions from individual units (or 
multiple units with a common stack) exceeded the opacity standard due 
to non-exempt reasons during the calendar quarter. As a check on the 
quarterly calculations from the source, this program also calculates 
the percentage of operating time that the opacity of emissions from 
individual units exceeded the opacity standard for any reason. With 
this program, ADEM compares the performance of each unit to the 
historical performance of that unit as well as compares it to the 
performance of the other units at that plant and other similar plants 
in the State, and the performance of the unit to the two percent 
threshold in the Alabama submittal. If the performance of a unit is not 
consistent with its historical performance or the performance of other 
similar units in the State, ADEM can review the daily exceedances of 
the opacity standard for the unit in question to determine if the 
exceedances were sporadic, or grouped in consecutive hours or 
consecutive days. ADEM may also ask the company for a detailed 
explanation of the exceedances (or a subset of exceedances) during the 
calendar quarter. If, for a source subject to the new standard, the 
number of unexcused opacity exceedances is in excess of two percent of 
the source operating time for which the opacity standard was applicable 
during the quarter, formal enforcement action may proceed.
    Opacity limitations have typically accompanied periodic Reference 
Method 5 particulate matter compliance tests (Method 5 tests) in SIPs. 
That is, where Method 5 tests are used to demonstrate compliance with 
filterable PM mass emission limitations, opacity limits and associated 
monitoring are commonly used as an indirect monitor for PM emissions 
and as indicators of good PM control equipment operation during the 
periods between Method 5 tests. EPA has long recognized opacity 
monitoring as a method of ensuring proper control device operation. See 
39 FR 9308, 9309 (Mar. 8, 1974) (NSPS Additions and Miscellaneous 
Amendments discussing opacity as an indicator of whether control 
equipment is properly maintained and operated).
    With use of continuous opacity monitors it is possible to have a 
continuous stream of opacity data. This results in the collection of 
many individual, short-term opacity measurements that reflect the full 
range of control device operating variability and, depending upon the 
amount of variability, may or may not be indicative of poor operation 
of control equipment and excess PM emissions. For example, coal-fired 
power generation facilities may experience sporadic opacity exceedances 
caused by variations in the constituents of coal burned. The revised 
Alabama rule shifts emphasis from isolated six-minute periods to longer 
periods that are more indicative of excess PM emissions and problems 
with operation and maintenance of control devices. As noted above, 
under the proposed revised rule, with the changes discussed in this 
action, an emissions unit is allowed: (1) Up to 100 percent opacity 
during 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; (2) up to 100 percent 
opacity for up to two percent of the operating time on a quarterly 
basis (less the exempted periods approved by ADEM's Director and 
included in a state-issued permit), for no more than 10 percent of the 
time on a daily basis; and (3) up to 20 percent opacity for the rest of 
the time in a quarter. EPA believes this approach, along with the 
monitoring and oversight safeguards discussed above, make appropriate 
use of COMS data for ensuring compliance with PM limits.

[[Page 18430]]

IV. What Does the Visible Emissions Rule in the Current SIP Require, 
and What Changes Are Requested by ADEM?

    The subject Visible Emissions rule is in Chapter 335-3-4 (``Control 
of Particulate Emissions'') of the Alabama SIP. The currently approved 
Alabama Rule 335-3-4-.01, ``Visible Emissions,'' has a generally 
applicable limit of 20 percent on opacity level and provides that one 
six-minute period per hour of up to 40 percent opacity is exempted \1\ 
from the 20 percent limit. The Director of ADEM may also grant, as part 
of a permit issued by the State, exemptions to the 20 percent limit 
during startup, shutdown, load change and rate change or other short, 
intermittent periods that are in addition to the hourly six-minute 40 
percent exemption. These exemptions are provided by subparagraphs 
(1)(b) and (1)(c), respectively. Additional exemptions for 
circumstances not relevant to this rulemaking are provided by 
subparagraphs (1)(d) \2\ and (1)(e).\3\ The text of the current rule 
reads, in relevant part, as follows:
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    \1\ Alabama Rule 335-3-4-.01, ``Visible Emissions,'' provides 
four specific ``exceptions'' to compliance with the generally 
applicable opacity limit at subparagraphs 335-3-4-.01(b), (c), (d), 
and (e). To be consistent with more common terminology, in this 
notice we refer to these as ``exemptions.''
    \2\ Subparagraph (d) provides that ADEM's Director may approve 
exceptions to this Rule in the form of source-specific adjustments 
to the opacity standard, provided certain conditions are met 
demonstrating to the Director's satisfaction that, with the 
adjustment, the source would continue to comply with its SIP 
particulate matter mass emissions limit.
    \3\ Subparagraph (e) provides that the provisions of this Rule 
do not apply to combustion sources in single-family and duplex 
dwellings where such sources are used for heating or other domestic 
purposes.

    (1) Visible Emissions Restrictions for Stationary Sources.
    (a) Except as provided in subparagraphs (b), (c), (d), or (e) of 
this paragraph, no person shall discharge into the atmosphere from 
any source of emission, particulate of an opacity greater than that 
designated as twenty percent (20%) opacity, as determined by a six 
(6) minute average.
    (b) During one six (6) minute period in any sixty (60) minute 
period, a person may discharge into the atmosphere from any source 
of emission, particulate of an opacity not greater than that 
designated as forty percent (40%) opacity.
    (c) The Director may approve exceptions to this Rule or specific 
sources which hold permits under Chapter 335-3-14; provided however, 
such exceptions may be made for startup, shutdown, load change, and 
rate change or other short, intermittent periods of time upon terms 
approved by the Director and made a part of such permit.
* * * * *
    (2) Compliance with opacity standards in this Rule shall be 
determined by conducting observations in accordance with Reference 
Method 9 in Appendix A, 40 CFR Part 60, as the same may be amended 
requiring a six (6) minute average as determined by twenty-four (24) 
consecutive readings, at intervals of fifteen (15) seconds each.

    The 2003 ADEM submittal would add three new paragraphs, (3), (4), 
and (5), to Alabama Rule 335-3-4-.01 that apply only to those emissions 
units that use COMS for measuring opacity, that operate such systems 
according to Federal specifications, and that are subject only to those 
opacity limits of the State's SIP (e.g., not subject to opacity limits 
under any preconstruction permit or other regulation). The revision 
provides that these units will not be in violation of the State's 
generally applicable opacity limitation if the non-exempt excess 
emissions periods do not exceed two percent of the source operating 
hours for which the opacity standard is applicable and for which the 
COMS is indicating valid data, on a quarterly basis. The text of the 
proposed change reads as follows:

    (3) The conditions in paragraph (4) of this Rule apply to each 
emissions unit that meets all of the following requirements:
    (a) A Continuous Opacity Monitoring System (COMS) is used for 
indication of opacity of emissions;
    (b) With respect to opacity limitations, the units are subject 
only to the opacity provisions stated in paragraph (1) of this Rule; 
and
    (c) The COMS system utilized is required to comply with the 
requirements of 40 CFR 60.13 or 40 CFR 75.14 (if applicable) and is 
required to be certified in accordance with the requirements of 40 
CFR 60, Appendix B, Performance Specification 1.
    (4) During each calendar quarter, the permittee will not be 
deemed in violation of Rule 335-3-4-.01(1) if the non-exempt excess 
emissions periods do not exceed 2.0 percent of the source operating 
hours for which the opacity standard is applicable and for which the 
COMS is indicating valid data.
    (5) Nothing in paragraph (4) of this Rule shall be construed to 
supercede the validity of opacity readings taken under paragraph (2) 
of this Rule.

    In summary, under the 2003 submission, sources operating COMS would 
not be deemed in violation of the standard where emissions in excess of 
the 20 percent opacity were limited to: (1) One six-minute average per 
hour of up to 40 percent opacity; (2) 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; and (3) no more than two percent of the remaining operating 
time after subtracting out all periods qualifying under the previous 
two instances.

V. What Changes Does EPA Recommend to the Submittal?

    As described above, under the Alabama SIP, Method 9 is the method 
specified for determining compliance with the 20 percent opacity limit. 
COMS are not specified as the method to determine compliance with the 
numerical opacity limit, although COMS data can be credible evidence of 
opacity. Opacity, both as measured by Method 9 and COMS, has been used 
as a proxy for particulate emissions and to indicate whether a company 
is following good air pollution control practices. ADEM has proposed 
amending its SIP to allow up to two percent of COMS readings to exceed 
20 percent opacity during non-exempt periods, in part since the Alabama 
SIP provides no other exemption from the standard for malfunction.
    The use of COMS increases data availability and provides a greater 
degree of reliability compared to the Method 9 procedure. Nonetheless, 
as currently written, the revision would allow a source to emit at a 
higher allowable average opacity percent level (as measured by COMS in 
six-minute increments) on a quarterly basis as well as allowing higher 
short term excursions than the current approved SIP allows. Because 
this potential for higher average opacity on a quarterly basis could 
indicate an increase in particulate matter emissions, and in the 
absence of a supporting demonstration of compliance with CAA 
requirements from the State, we believe that the 2003 SIP submittal is 
not approvable as submitted. The submission is also not clear about 
whether the new opacity standard for certain sources with COMS at 335-
3-4-.01(3)-(5) applies in addition to, or in lieu of, the existing 
opacity standard in paragraphs 335-3-4-.01(1)(a)-(b), as measured under 
paragraph 335-3-4-.01(2). In addition, the purpose behind new paragraph 
335-3-4-.01(5) is not clear.
    EPA believes the State can revise the 2003 ADEM submittal by 
amending it to ensure that the allowable average quarterly opacity is 
at least as stringent as (i.e., equal to or lower than) that allowed by 
the current approved SIP, and by being clear that only a single version 
of the standard applies to any unit (although any credible evidence of 
opacity could be used to assess compliance with the applicable version 
of the standard). Accordingly, this proposed approval is contingent 
upon Alabama's submission of a revised rule with certain changes. The 
revision

[[Page 18431]]

would clearly indicate that a unit is covered by either the existing 
opacity standard at paragraphs 335-3-4-.01(1)(a)-(b), as measured under 
paragraph 335-3-4-.01(2), or by the new standard established in 
paragraphs 335-3-4-.01(1)(a), (3)-(4), as measured by the COMS 
referenced in those paragraphs--but not both.\4\ The revision would 
also provide that the hourly 40 percent exemption under Alabama rule 
335-3-4-.01(1)(b) does not apply to sources subject to the new 
paragraphs 335-3-4-.01(3) and 335-3-4-.01(4). Thus, the 40 percent 
exemption for up to 24 six-minute periods per day on an hourly basis 
would be replaced by the generally applicable 20 percent standard. The 
revision would allow a source to exceed the 20 percent standard (up to 
100 percent opacity) during no more than 24 six-minute periods per day. 
In part this revision would replace the existing provision allowing one 
six-minute exceedance per hour at 40 percent opacity with a provision 
allowing up to 24 six-minute exceedances per calendar day at 100 
percent opacity. However, under the revised provision, these 
exceedances would be part of, not in addition to, the exceedances 
allowed under 335-3-4-.01(4) (i.e., two percent of operating time).
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    \4\ As noted elsewhere, the exemptions in paragraphs 335-3-
4-.01(1)(c)-(e) are not impacted by the 2003 SIP revision and would 
continue to apply to either the existing or the revised standard.
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    Thus, under the current SIP, a source is required to maintain 20 
percent opacity, except that it may emit at up to 40 percent opacity 
for one six-minute average per hour, and may have emissions of up to 
100 percent opacity as specified in a permit. Under the 2003 
submission, certain sources using COMS would, in addition to the 
current SIP exemptions, also be allowed emissions of up to 100 percent 
opacity for up to two percent of the quarterly operating time that they 
are otherwise subject to the 20 percent opacity limit. Under the 
revision proposed for approval in this notice, these sources still 
would be allowed emissions of up to 100 percent opacity for up to two 
percent of quarterly operating time that they are subject to the 20 
percent opacity limit (but not to exceed 10 percent of a calendar day), 
and they would not be allowed the 40 percent hourly exemption.\5\
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    \5\ Although this new opacity standard would only apply to 
certain sources using COMS, EPA notes that, consistent with EPA's 
and ADEM's credible evidence rules, nothing in the rule should 
preclude the use of COMS to enforce the existing standard or the use 
of Method 9 to enforce the new standard.
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    Where currently any source may exceed the opacity limit for six 
minutes out of every hour (i.e., 10 percent of the time, on an hourly 
basis), under the revision EPA is proposing would be approvable, a 
source using COMS subject to the new standard could exceed the opacity 
limit for 10 percent of the time on a daily basis (i.e., up to 2.4 
hours of consecutive opacity exceedances per calendar day), but for 
only two percent of the time on a quarterly basis. Under the current 
standard, the 40 percent opacity limit in theory allows a source to 
emit a total of approximately 219 hours of emissions in a quarter at up 
to 40 percent opacity, if the source uses one six-minute exemption for 
every hour of operation. Under the proposed revision, a source would be 
allowed to emit no more than 44 hours of excess emissions in a quarter 
(and no more than 2.4 hours in a day), but those emissions could have 
up to 100 percent opacity.\6\
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    \6\ The director's discretion provisions under Alabama rule 335-
3-4-.01(1)(c) and (d) would be unchanged by this SIP revision, so 
periods of excess emissions allowed in a permit pursuant to those 
provisions would continue to be allowed, in addition to the 
emissions allowed by the new provisions discussed herein. EPA notes 
that, as the director's discretion provisions are not being revised 
by ADEM or reviewed by EPA at present, nothing in this notice should 
be considered as approving those provisions.
---------------------------------------------------------------------------

    As a result, the final rule would have the potential to increase 
the impact of opacity exceedances on a short-term basis by allowing 
exceedances of up to 100 percent opacity and also allowing those 
periods of excess opacity to be aggregated in up to 24 consecutive six-
minute periods per day (as opposed to the current approved rule which 
provides an hourly 40 percent exemption, also for a total of 24 six-
minute periods per day). However, the long-term cap of two percent 
serves to restrict the total amount of time a source is allowed to 
exceed the standard. As discussed below, EPA believes that the 
reduction in total duration of exceedances will reduce average opacity 
as compared to the current standard, even taking into consideration 
that the exemption in the current standard limits exceedances to 40 
percent (not 100 percent) opacity.
    Thus, under the proposed revised rule, with the changes discussed 
in this notice, an emissions unit covered by the new standard would be 
allowed: (1) Up to 100 percent opacity during 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; (2) up to 100 percent opacity for up to two percent of 
the operating time on a quarterly basis (where the amount of operating 
time does not include the exempted periods approved by ADEM's Director 
and included in a state-issued permit), but for no more than ten 
percent of the time on a daily basis; and (3) up to 20 percent opacity 
for the rest of the time in a quarter. The current federally-approved 
SIP opacity limit remains in effect. Any new exceptions proposed in 
this action do not take effect until EPA takes final action. 
Furthermore, any final rule would be prospective only. In addition, 
this proposal is not intended to affect on-going enforcement actions 
against sources that may be subject to the new standard, nor does it 
relieve affected sources in Alabama of their obligations to comply with 
any other federal, state, or local opacity requirements, or particulate 
matter control requirements.

VI. What Technical Analysis Was Used To Support Approval of This SIP 
Revision?

    The existing Alabama SIP specifies Method 9 as the method for 
determining compliance with the generally applicable opacity limit for 
sources of PM emissions. See Ala. Admin. Code r. 335-3-4-.01(2). More 
frequent readings with COMS help determine whether a source is 
following good air pollution control practices between Method 9 or 
Method 5 tests. With the additional restrictions described above, the 
proposed SIP revision can be shown to be no less stringent in terms of 
average quarterly opacity than the existing SIP.
    Today, we propose to approve Alabama's SIP revision contingent upon 
the revision including our recommended changes, based on a finding that 
the revision would not increase average quarterly opacity levels and 
thus would not interfere with attainment or maintenance of a NAAQS, 
RFP, or any other requirement of the Act. The relationship between 
changes in opacity and increases or decreases in ambient 
PM2.5 levels cannot be quantified readily and is 
particularly uncertain for short term and site-specific analyses. There 
are several contributors to this uncertainty 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 in one may not track 
fluctuations in the other, and (4) differences between what the ambient 
sampler collects and the mass of particles that exists at the point

[[Page 18432]]

of COMS measurement (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).
    In addition to these uncertainty factors, opacity is directly 
related to particle size, with particles of an aerodynamic diameter of 
approximately 1.0 micrometer having the greatest potential for 
impairment of visibility, or increased opacity. (See, e.g., Malm, 
William C. ``Introduction to Visibility,'' Cooperative Institute for 
Research in the Atmosphere, May 1999, Chap. 2, p. 8). As particles 
increase in size, their impact on opacity diminishes, despite the fact 
that their mass may increase. Thus for PM emissions of a given mass 
level, opacity can be greater or less depending on the particle size 
distribution.
    Several past instances and State and Federal rules are instructive 
regarding the uncertainties in relating opacity to PM concentrations. 
EPA recognized and accounted for these uncertainties as early as the 
1970s by permitting sources to adjust source-specific opacity standards 
under new source performance standards (NSPS) when they could 
demonstrate that they were in compliance with applicable PM limits at 
times when opacity limits were being exceeded. See, e.g., 44 FR 37960, 
37961 (June 29, 1979). In EPA's own NSPS for glass manufacturing 
plants, (40 CFR 60.293(e)), and national emission standard for 
Inorganic Arsenic Emissions from Glass Manufacturing Plants (40 CFR 
61.163), EPA has written specific provisions into its standards 
permitting source owners or operators to redetermine opacity 
limitations where they can demonstrate compliance with emission limits 
in the applicable rules. More recently, when examining a study of COMS 
at a portland cement kiln, we have found that the plant's visible 
emissions readings were consistently below its allowable limit (20 
percent) while PM emissions significantly exceeded the NSPS due to 
broken bags in its baghouse. Finally, a number of States have 
incorporated similar provisions into their regulations. (See, e.g., 
Indiana Administrative Code, 326 IAC 5-1-5(b); Wisconsin NR 431.07; 
Pima County, Arizona 2-8-300(C)).
    The contributions to uncertainty described above lessen when 
applied to longer term averages and the relationship between ambient 
PM2.5 measurements and changes in opacity are more reliable 
than for shorter term (e.g., daily) assessments. Therefore, for 
purposes of this proposal, EPA focused on analyzing the effects of the 
proposed change in the opacity limitations for facilities covered by 
the rule over quarterly periods. EPA believes that a quarterly basis is 
appropriate because correlations between opacity and PM control device 
operation are more readily generalized over a longer-term basis and, 
therefore, a quarterly average is more likely to reflect impacts on the 
ambient PM levels accurately than a daily average, and because ADEM's 
proposed rule includes a quarterly limit. By calculating and comparing 
the average quarterly opacities allowed by the current SIP approved 
rule, the 2003 ADEM submittal, and the 2003 ADEM submittal with 
required changes specified, we can determine which proposed SIP change, 
if any, provides an average quarterly opacity equivalent with, or more 
stringent than, the average quarterly opacity allowed by the current 
SIP approved rule. Proposed changes that provide average quarterly 
opacities more stringent than (or equivalent with) those allowed by the 
existing SIP rule are expected to be more stringent than (or equivalent 
to) the existing SIP rule.
    EPA is not performing similar calculations comparing stringency of 
average daily opacity levels under the current rule and the proposed 
rule because a generally applicable relationship between opacity and PM 
mass emissions cannot be specified over short averaging times (e.g., 24 
hours or less). Even with extensive testing, it is very difficult to 
establish reliable correlations between the magnitude of opacity 
measurements and PM mass emissions for short averaging times (e.g., 24 
hours or less) that will remain reliable over a longer period of record 
(i.e., that will establish a direct daily correlation over a longer 
period, such as three or more months). Therefore, opacity may not be a 
reliable indicator of short-term emissions, or for use in projecting 
changes in short-term PM ambient air quality concentrations. 
Accordingly, we conclude that the proposed change in the allowed 
opacity will have no effect on attainment of the 24-hour PM NAAQS (35 
[mu]g/m3 for PM2.5 and 150 [mu]mg/m3 
for PM10) or (based on the quarterly stringency comparison) 
the annual PM NAAQS (15.0 [mu]g/m for PM2.5).
    We can calculate the average allowable quarterly opacity for a unit 
by multiplying an allowed level of opacity by the duration for which 
that level of opacity is allowed, summing those products for each 
allowed level of opacity occurring over a quarter, and then dividing 
that total by the number of six-minute periods in a quarter. The 
average quarterly opacity for a unit is an opacity value equivalent 
with one single, constant opacity value emitted for each and every six-
minute period of the quarter, allowing us to compare a unit with a 
longer period of lower opacity to one with a shorter period of higher 
opacity.
    The general formula for calculating the allowable average quarterly 
opacity (i.e., the average opacity (percent) allowed by rule over a 
quarter) is:
[GRAPHIC] [TIFF OMITTED] TP12AP07.010

Where:
n = specific period of quarterly operation,
opacity = opacity (percent) related to that specific period,
duration = number of six-minute average periods related to the 
specific period, and
21,900 = number of six-minute average periods per quarter.

    For the Alabama analysis, using the above general formula to 
determine the allowable average opacity over a quarter, we chose to use 
the maximum opacity allowed for each condition, the maximum duration 
allowed for each condition, and the maximum amount of time for unit 
operation when calculating the average allowable quarterly opacity. 
Although operation with opacity at the maximum level for the longest 
period allowed under a rule is not reflective of actual operations, 
such a conservative assumption provides a consistent basis for 
comparisons.
    Usually calculation of allowable average quarterly opacity can be 
readily ascertained, since opacity limits and their associated 
condition durations are known explicitly. However, because ADEM allows 
an exemption from opacity limits during periods of startup, shutdown, 
load change and rate change or other short, intermittent periods upon

[[Page 18433]]

terms approved by ADEM's Director and included in a state-issued 
permit, and because the duration of those periods is not known, we used 
a variable, T1, to represent the duration of those periods. 
In theory, the duration of those periods could range from 0, meaning no 
periods of exemption for a quarter, to 21,900, meaning all periods of 
the quarter are exempt.\7\ In practice, one sample of units subject to 
the current SIP rule contains durations of about 400 periods per 
quarter for this exemption.
---------------------------------------------------------------------------

    \7\ EPA does not intend to indicate that it would be appropriate 
or consistent with the SIP for an exemption period under 335-3-
4.01(1)(c) to last for an extended period of time, but rather is 
utilizing conservative assumptions for the purpose of ensuring the 
requirements of section 110(l) will be met. EPA does not anticipate 
that a source would, in fact, operate at 100% opacity for all 
permissible excursion periods.
---------------------------------------------------------------------------

    Relying on the variable T1, calculation of allowable 
average quarterly opacities becomes straightforward. By way of example, 
the allowable average quarterly opacity for the 2003 ADEM Submittal is 
the sum of the ten percent of the quarter's duration at 40 percent 
opacity, the time (T1) at 100 percent opacity due to 
exemptions, the two percent of the non-exempt time of the quarter's 
duration at 100 percent opacity, and the balance of the non-exempt time 
of the quarter's duration at 20 percent opacity, all divided by the 
number of six-minute periods in the quarter. The equation shown below 
provides the allowable average quarterly opacity for the 2003 ADEM 
Submittal for T1 values of 0 to 19,710:
[GRAPHIC] [TIFF OMITTED] TP12AP07.011

    We derived allowable average quarterly opacity equations for the 
current SIP-approved rule and the 2003 ADEM submittal, substituted 
various exemption durations (T1) in the equations, 
determined the corresponding allowable average quarterly opacities, and 
organized the results as shown in Table 1 below.

Table 1.--Calculated Allowable Average Quarterly Opacity Levels, for Various Startup, Shutdown, Load Change, and
       Rate Change Durations (T1), Using Alabama's Current SIP-Approved Rule, and the 2003 ADEM Submittal
----------------------------------------------------------------------------------------------------------------
                                        Calculated allowable average quarterly opacity (percent) for various
                                            startup, shutdown, load change and rate change durations (T1)
                                   -----------------------------------------------------------------------------
                                       T1 = 0     T1 = 1,000  T1 = 10,000  T1 = 17,520  T1 = 19,710  T1 = 21,900
----------------------------------------------------------------------------------------------------------------
Current SIP Approved Rule.........        22.00        25.65        58.53        86.00        94.00       100.00
2003 ADEM Submittal...............        23.44        27.02        59.24        86.16        94.00       100.00
----------------------------------------------------------------------------------------------------------------

    As can be seen, under these conservative assumptions, the 2003 ADEM 
submittal would result in allowable average quarterly opacity levels 
that are slightly higher than those calculated from the current SIP 
rule for periods of startup, shutdown, load change and rate change, 
i.e. for where those durations are less than 19,710 six-minute 
averages.
    In order to be approvable, we have recommended that ADEM eliminate 
the exemption for six-minutes at up to 40 percent opacity for up to ten 
percent of the operating time. The allowable average quarterly opacity 
for the 2003 ADEM Submittal With Required Changes Specified for all 
T1 values =
[GRAPHIC] [TIFF OMITTED] TP12AP07.012

    We derived allowable average quarterly opacity equations for the 
current SIP approved rule and the 2003 ADEM submittal with recommended 
changes specified, substituted various exemption durations 
(T1) in the equations, determined the corresponding 
allowable average quarterly opacities, and organized the results as 
shown in Table 2 below. As shown, the proposed revision to the SIP rule 
yields an allowable average quarterly opacity equivalent to or less 
than the allowable average quarterly opacity calculated from the 
current SIP rule in all cases.

[[Page 18434]]

Table 2.--Calculated Allowable Average Quarterly Opacity Levels, for Various Startup, Shutdown, Load Change, and
    Rate Change Durations (T1), Using Alabama's Current SIP-Approved Rule and the Proposed SIP Revision With
                                          Recommended Changes Specified
----------------------------------------------------------------------------------------------------------------
                                        Calculated allowable average quarterly opacity (percent) for various
                                            startup, shutdown, load change and rate change durations (T1)
                                   -----------------------------------------------------------------------------
                                       T1 = 0     T1 = 1,000  T1 = 10,000  T1 = 17,520  T1 = 19,710  T1 = 21,900
----------------------------------------------------------------------------------------------------------------
Current SIP Approved Rule.........        22.00        25.65        58.53        86.00        94.00       100.00
2003 ADEM Submittal with                  21.60        25.18        57.40        84.32        92.16       100.00
 Recommended Changes Specified....
----------------------------------------------------------------------------------------------------------------

    Therefore, by incorporating these recommended changes, Alabama 
would reduce uncertainties related to whether such a change could 
interfere with attainment, RFP or any other requirement of the Act. 
Accordingly, we conclude that the revision of Alabama's SIP rule to 
incorporate the 2003 ADEM submittal with our recommended changes 
specified in this action would not interfere with requirements of the 
CAA and would be approvable. Further details of this analysis are 
contained in the technical support document.

VII. What Happens Next?

    EPA anticipates Alabama will submit a revised rule revision 
reflecting the changes discussed in section IV above. If Alabama's 
revised rule is submitted and considered approvable, after considering 
any comments received on today's proposed approval, EPA will publish a 
final rule in the Federal Register approving the State's requested rule 
revision and will also address in that rulemaking any comments received 
on this proposed approval. In addition, we plan to develop further 
criteria to aid EPA Regional Offices in evaluating future revisions to 
rules such as Alabama's and, in this regard, we expect to publish in 
the near future a request for information that will assist us in that 
effort.

VIII. Proposed Action

    EPA is proposing to approve the Visible Emissions portion of a SIP 
revision submitted to EPA by Alabama on September 11, 2003, provided it 
is revised as described in section IV of this action and submitted as a 
SIP revision in accordance with the requirements of the CAA.

IX. Statutory and Executive Order Reviews

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), this 
proposed action is not a ``significant regulatory action'' and 
therefore is not subject to review by the Office of Management and 
Budget. For this reason, this action is also not subject to Executive 
Order 13211, ``Actions Concerning Regulations That Significantly Affect 
Energy Supply, Distribution, or Use'' (66 FR 28355, May 22, 2001). This 
proposed action merely proposes to approve state law as meeting Federal 
requirements, and imposes no additional requirements beyond those 
imposed by state law. Accordingly, I hereby certify that this proposed 
rule will not have a significant economic impact on a substantial 
number of small entities under the Regulatory Flexibility Act (5 U.S.C. 
601 et seq.). Because this action proposes to approve requirements 
under state law and does not impose any additional enforceable duty 
beyond that required by state law, it does not contain any unfunded 
mandate or significantly or uniquely affect small governments, as 
described in the Unfunded Mandates Reform Act of 1995 (Public Law 104-
4).
    This proposed rule also does not have tribal implications because 
it will not have a substantial direct effect on one or more Indian 
tribes, on the relationship between the Federal Government and Indian 
tribes, or on the distribution of power and responsibilities between 
the Federal Government and Indian tribes, as specified by Executive 
Order 13175 (65 FR 97249, November 9, 2000). This proposed action also 
does not have Federalism implications because it does not have 
substantial direct effects on the States, on the relationship between 
the national government and the States, or on the distribution of power 
and responsibilities among the various levels of government, as 
specified in Executive Order 13132 (64 FR 43255, August 10, 1999). This 
action merely proposes to approve State rule as consistent with Federal 
standards, and does not alter the relationship or the distribution of 
power and responsibilities established in the CAA. This proposed rule 
also is not subject to Executive Order 13045, ``Protection of Children 
from Environmental Health Risks and Safety Risks'' (62 FR 19885, April 
23, 1997), because it is not economically significant.
    In reviewing SIP submissions, EPA's role is to approve state 
choices, provided that they meet the criteria of the CAA. In this 
context, in the absence of a prior existing requirement for the state 
to use voluntary consensus standards (VCS), EPA has no authority to 
disapprove a SIP submission for failure to use VCS. It would thus be 
inconsistent with applicable law for EPA, when it reviews a SIP 
submission to use VCS in place of a SIP submission that otherwise 
satisfies the provisions of the CAA. Thus, the requirements of section 
12(d) of the National Technology Transfer and Advancement Act of 1995 
(15 U.S.C. 272 note) do not apply. This proposed rule does not impose 
an information collection burden under the provisions of the Paperwork 
Reduction Act of 1995 (44 U.S.C. 3501 et seq.).

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Carbon monoxide, 
Intergovernmental relations, Nitrogen dioxide, Ozone, Particulate 
matter, Reporting and recordkeeping requirements, Sulfur oxides, 
Volatile organic compounds.

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

    Dated: April 4, 2007.
J.I. Palmer, Jr.,
Regional Administrator, Region 4.
[FR Doc. E7-6948 Filed 4-11-07; 8:45 am]

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