Federal Implementation Plan for the Billings/Laurel, MT, Sulfur Dioxide Area, 21418-21465 [E8-7868]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 73, Number 77 (Monday, April 21, 2008)]
[Rules and Regulations]
[Pages 21418-21465]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E8-7868]



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Part II





Environmental Protection Agency





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40 CFR Part 52



Federal Implementation Plan for the Billings/Laurel, Montana, Sulfur 
Dioxide Area; Final Rule

Federal Register / Vol. 73, No. 77 / Monday, April 21, 2008 / Rules 
and Regulations

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2006-0098; FRL-8551-2]
RIN 2008-AA01


Federal Implementation Plan for the Billings/Laurel, MT, Sulfur 
Dioxide Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is promulgating a 
Federal Implementation Plan (FIP) containing emission limits and 
compliance determining methods for several sources located in Billings 
and Laurel, Montana. EPA is promulgating a FIP because of our previous 
partial and limited disapprovals of the Billings/Laurel Sulfur Dioxide 
(SO2) State Implementation Plan (SIP). The intended effect of this 
action is to assure attainment of the SO2 National Ambient Air Quality 
Standards (NAAQS) in the Billings/Laurel, Montana area. EPA is taking 
this action under sections 110, 301, and 307 of the Clean Air Act 
(Act).

DATES: Effective Date: This final rule is effective May 21, 2008. The 
incorporation by reference of certain publications listed in this 
regulation is approved by the Director of the Federal Register as of 
May 21, 2008.

ADDRESSES: EPA has established a docket for this action under Docket ID 
No. EPA-R08-OAR-2006-0098. All documents in the docket are listed on 
the https://www.regulations.gov Web site. Although listed in the index, 
some information is not publicly available, e.g., 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 https://www.regulations.gov or in hard copy at 
the Air and Radiation Program, Environmental Protection Agency (EPA), 
Region 8, 1595 Wynkoop Street, Denver, Colorado 80202-1129. EPA 
requests that if at all possible, you contact the individual listed in 
the FOR FURTHER INFORMATION CONTACT section to view the hard copy of 
the docket. You may view the hard copy of the docket Monday through 
Friday, 8 a.m. to 4 p.m., excluding Federal holidays.

FOR FURTHER INFORMATION CONTACT: Laurie Ostrand, Air and Radiation 
Program, Environmental Protection Agency (EPA), Region 8, 1595 Wynkoop 
Street, Denver, Colorado 80202-1129, (303) 312-6437, 
ostrand.laurie@epa.gov.

SUPPLEMENTARY INFORMATION: 

Table of Contents

Definitions

I. Background of the Final Rules
II. Issues Raised by Commenters and EPA's Response
    A. FIP Not Necessary
    B. EPA Exceeded Its Authority in Proposing a FIP
    C. Flare Monitoring
    D. Flare Limits
    E. Concerns With Dispersion Modeling
    F. Miscellaneous Comments
    G. MSCC Specific Issues
    H. ConocoPhillips Specific Issues
    I. ExxonMobil Specific Issues
    J. CHS Inc. Specific Issues
III. Summary of the Final Rules and Changes From the July 12, 2006, 
Proposal
    A. Flare Requirements Applicable to All Sources
    B. CHS Inc.
    C. ConocoPhillips
    D. ExxonMobil
    E. Montana Sulphur & Chemical Company (MSCC)
    F. Modeling to Support Emission Limits
IV. Statutory and Executive Order Reviews
    A. Executive Order 12866, Regulatory Planning Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    E. Executive Order 13132, Federalism
    F. Executive Order 13175, Coordination With Indian Tribal 
Governments
    G. Executive Order 13045, Protection of Children From 
Environmental Health Risks and Safety Risks
    H. Executive Order 13211, Actions That Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act
    L. Petitions for Judicial Review

Definitions

    For the purpose of this document, we are giving meaning to certain 
words or initials as follows:
    (i) The words or initials Act or CAA mean or refer to the Clean Air 
Act, unless the context indicates otherwise.
    (ii) The initials API mean or refer to the American Petroleum 
Institute.
    (iii) The initials BAAQMD mean or refer to the Bay Area Air Quality 
Management District.
    (iv) The initials CEMS mean or refer to continuous emission 
monitoring system.
    (v) The initials CO mean or refer to carbon monoxide.
    (vi) The initials COPC mean or refer to ConocoPhillips.
    (vii) The words EPA, we, us or our mean or refer to the United 
States Environmental Protection Agency.
    (viii) The initials FIP mean or refer to Federal Implementation 
Plan.
    (ix) The initials H2S mean or refer to hydrogen sulfide.
    (x) The initials MBER mean or refer to the Montana Board of 
Environmental Review.
    (xi) The initials MDEQ mean or refer to the Montana Department of 
Environmental Quality.
    (xii) The initials MPA mean or refer to the Montana Petroleum 
Association.
    (xiii) The initials MSCC mean or refer to the Montana Sulphur & 
Chemical Company.
    (xiv) The initials NAAQS mean or refer to National Ambient Air 
Quality Standards
    (xv) The initials NEDA/CAP mean or refer to the National 
Environmental Development Association's Clean Air Project.
    (xvi) The initials NPRA mean or refer to the National Petrochemical 
& Refiners Association.
    (xvii) The initials SCAQMD mean or refer to the South Coast Air 
Quality Management District.
    (xviii) The initials SIP mean or refer to State Implementation 
Plan.
    (xix) The initials SO2 mean or refer to sulfur dioxide.
    (xx) The words State or Montana mean the State of Montana, unless 
the context indicates otherwise.
    (xxi) The initials SRU mean or refer to sulfur recovery unit.
    (xxii) The initials SWS mean or refer to sour water stripper.
    (xxiii) The initials WETA mean or refer to the Western 
Environmental Trade Association.
    (xxiv) The initials WSPA mean or refer to the Western States 
Petroleum Association.
    (xxv) The initials YCC mean or refer to the Yellowstone County 
Commissioners.
    (xxvi) The initials YVAS mean or refer to the Yellowstone Valley 
Audubon Society.

I. Background of the Final Rules

    The Clean Air Act (Act) requires EPA to establish national ambient 
air quality standards (NAAQS) that protect public health and welfare. 
NAAQS have been established for SO2 as follows: 0.030 parts 
per million (ppm) annual standard, not to be exceeded in a calendar 
year; 0.14 ppm 24-hour standard, not to be exceeded more than once per 
calendar year; and 0.5 ppm 3-hour standard, not to be exceeded more

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than once per calendar year. See 40 CFR 50.4 and 50.5. The Act also 
requires states to prepare and gain EPA approval of a plan, termed a 
State Implementation Plan (SIP), to assure that the NAAQS are attained 
and maintained.
    Dispersion modeling completed in 1991 and 1993 for the Billings/
Laurel area of Montana predicted that the SO2 NAAQS were not 
being attained. As a result, in March 1993 EPA (pursuant to sections 
110(a)(2)(H) and 110(k)(5) of the Act, 42 U.S.C. 7410(a)(2)(H) and 
7410(k)(5)) requested the State of Montana to revise its previously 
approved SO2 SIP for the Billings/Laurel area. See 58 FR 
41450, August 4, 1993. In response, the State submitted revisions to 
the SO2 SIP on September 6, 1995, August 27, 1996, April 2, 
1997, July 29, 1998, and May 4, 2000.
    On May 2, 2002 (67 FR 22168) and May 22, 2003 (68 FR 27908), we 
partially approved, partially disapproved, limitedly approved, and 
limitedly disapproved the Billings/Laurel SO2 SIP. In those 
actions we disapproved the following:
     The attainment demonstration due to issues with various 
emission limits, inappropriate stack height credit, and lack of 
emission limits on flares.
     The emission limits for Montana Sulphur & Chemical 
Company's (MSCC's) sulfur recovery unit (SRU) 100-meter stack and the 
stack height credit on which those limits were based.
     The emission limits for MSCC's auxiliary vent stacks due 
to lack of an adequate limit on fuel burned in the associated heaters 
and boilers and lack of a reliable compliance determining method.
     The emission limits for MSCC's 30-meter stack due to lack 
of an adequate limit on fuel burned in the associated heaters and 
boilers, and lack of a reliable compliance determining method.
     Provisions that allowed sour water stripper overheads to 
be burned in the flares at CHS Inc. and ExxonMobil.
     ExxonMobil's refinery fuel gas combustion device emission 
limits and associated compliance determining methods.
     ExxonMobil's Coker CO Boiler stack emission limits and 
associated compliance determining methods.
     CHS Inc.'s combustion source emission limits and certain 
associated compliance determining methods.
    On June 10, 2002, MSCC petitioned the United States Court of 
Appeals for the Ninth Circuit for review of EPA's May 2, 2002, final 
SIP action. Subsequently, MSCC and EPA agreed to a stay of the 
litigation pending EPA's final action on this FIP. The case is 
captioned Montana Sulphur & Chemical Company v. United States 
Environmental Protection Agency, No. 02-71657. No petitions for 
judicial review were filed regarding EPA's May 22, 2003, SIP action.
    On July 12, 2006 (71 FR 39259), EPA proposed Federal Implementation 
Plan (FIP) provisions for the Billings/Laurel, Montana area because of 
our disapproval of portions of Montana's Billings/Laurel SO2 
SIP. In our proposal, we indicated that our FIP would not replace the 
SIP entirely, but instead would only replace elements of, or fill gaps 
in, the SIP.
    In promulgating today's rules, EPA is fulfilling its mandatory duty 
under section 110(c) of the Act. Under section 110(c), whenever we 
disapprove a SIP, in whole or in part, we are required to promulgate a 
FIP. Specifically, section 110(c) provides:

    ``(1) The Administrator shall promulgate a Federal 
implementation plan at any time within 2 years after the 
Administrator--
    (A) Finds that a State has failed to make a required submission 
or finds that the plan or plan revision submitted by the State does 
not satisfy the minimum criteria established under [section 
110(k)(1)(A)],\1\ or
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    \1\ Section 110(k)(1) requires the Administrator to promulgate 
minimum criteria that any plan submission must meet before EPA is 
required to act on the submission. These completeness criteria are 
set forth at 40 CFR 51, Appendix V.
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    (B) Disapproves a State implementation plan submission in whole 
or in part, unless the State corrects the deficiency, and the 
Administrator approves the plan or plan revision, before the 
Administrator promulgates such Federal implementation plan.''
    Thus, because we disapproved portions of the Billings/Laurel 
SO2 SIP, and the attainment demonstration, we are required 
to promulgate a FIP.
    Section 302(y) defines the term ``Federal implementation plan'' in 
pertinent part, as:

    ``[A] plan (or portion thereof) promulgated by the Administrator 
to fill all or a portion of a gap or otherwise correct all or a 
portion of an inadequacy in a State implementation plan, and which 
includes enforceable emission limitations or other control measures, 
means or techniques (including economic incentives, such as 
marketable permits or auctions or emissions allowances) * * *.''

    More simply, a FIP is ``a set of enforceable federal regulations 
that stand in the place of deficient portions of a SIP.'' McCarthy v. 
Thomas, 27 F.3d 1363, 1365 (9th Cir. 1994). As the Court of Appeals for 
the D.C. Circuit noted in a 1995 case, FIPs are powerful tools to 
remedy deficient state action:

    The FIP provides an additional incentive for state compliance 
because it rescinds state authority to make the many sensitive 
technical and political choices that a pollution control regime 
demands. The FIP provision also ensures that progress toward NAAQS 
attainment will proceed notwithstanding inadequate action at the 
state level.

    Natural Resources Defense Council, Inc. v. Browner, 57 F.3d 1122, 
1124 (D.C. Cir. 1995).
    When EPA promulgates a FIP, courts have not required EPA to 
demonstrate explicit authority for specific measures: ``We are inclined 
to construe Congress' broad grant of power to the EPA as including all 
enforcement devices reasonably necessary to the achievement and 
maintenance of the goals established by the legislation.'' South 
Terminal Corp. v. EPA, 504 F.2d 646, 669 (1st Cir. 1974). As the Ninth 
Circuit stated in a case involving a FIP with far-reaching consequences 
in Los Angeles: ``The authority to regulate pollution carries with it 
the power to do so in a manner reasonably calculated to reach that 
end.'' City of Santa Rosa v. EPA, 534 F.2d 150, 155 (9th Cir. 1976), 
vacated and remanded on other grounds sub nom. Pacific Legal Foundation 
v. EPA, 429 U.S. 990 (1976).
    In addition to giving EPA remedial authority, section 110(c) 
enables EPA to assume the powers that the state would have to protect 
air quality, when the state fails to adequately discharge its planning 
responsibility. As the Ninth Circuit held, when EPA acts to fill in the 
gaps in an inadequate state plan under section 110(c), EPA `` `stands 
in the shoes of the defaulting State, and all of the rights and duties 
that would otherwise fall to the State accrue instead to EPA.' '' 
Central Arizona Water Conservation District v. EPA, 990 F.2d 1531, 1541 
(9th Cir. 1993). As the First Circuit held in an early case:

    ``[T]he Administrator must promulgate promptly regulations 
setting forth `an implementation plan for a State' should the state 
itself fail to propose a satisfactory one * * * The statutory scheme 
would be unworkable were it read as giving to EPA, when promulgating 
an implementation plan for a state, less than those necessary 
measures allowed by Congress to a state to accomplish federal clean 
air goals. We do not adopt any such crippling interpretation.''

    South Terminal Corp. v. EPA, supra, at 668 (citing previous version 
of section 110(c)).
    The Billings/Laurel SO2 FIP establishes emission limits 
and compliance determining methods for four sources located in 
Billings/Laurel, Montana, to replace/fill gaps in portions of the SIP 
we disapproved, and to

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support our attainment demonstration. Three of the sources are 
petroleum refineries: CHS Inc., ConocoPhillips (including the Jupiter 
Sulfur facility), and ExxonMobil. The fourth source is Montana Sulphur 
& Chemical Company, which provides sulfur recovery for the ExxonMobil 
refinery.
    The following is a summary of the major components of our FIP rule:
    (1) The FIP establishes flare emission limits at all four sources 
(150 lbs SO2/3-hour period at all but the Jupiter Sulfur 
flare, 75 lbs SO2/3-hour period shared limit for the Jupiter 
Sulfur flare and the Jupiter Sulfur SRU/ATS stack) and monitoring 
methods to determine compliance with those limits. The FIP includes an 
affirmative defense to penalties for violations of the flare limits 
that occur during malfunction, startup, and shutdown periods. To 
determine flare emissions, the FIP requires concentration monitoring 
(which can consist of continuous monitoring, grab sampling, or 
integrated sampling) and continuous flow monitoring.
    (2) The FIP prohibits the burning of sour water stripper overheads 
in CHS Inc.'s main crude heater and requires CHS Inc. to keep the valve 
between the old sour water stripper and the main crude heater closed, 
chained, and locked.
    (3) The FIP provides that emission limits for identified ExxonMobil 
refinery fuel gas combustion units are contained in the SIP, and 
establishes compliance determining methods for instances in which the 
H2S concentration in the refinery fuel gas stream exceeds 
1200 ppmv. These methods involve the use of length-of-stain detector 
tubes on a once-per-hour frequency.
    (4) The FIP provides that emission limits for ExxonMobil's Coker CO 
Boiler stack, when ExxonMobil's Coker unit is operating and Coker unit 
flue gases are burned in the Coker CO Boiler, are contained in the SIP. 
The FIP establishes compliance determining methods for these emission 
limits that require measurement of the SO2 concentration and 
flow rate in the Coker CO Boiler stack using CEMS.
    (5) The FIP establishes emission limits on MSCC's SRU 100-meter 
stack, based on good engineering practice (GEP) stack height credit of 
65 meters, with compliance with these limits to be determined using 
methods already approved in the SIP. The FIP does not provide variable 
emission limits for this stack.
    (6) The FIP establishes emission limits and compliance determining 
methods for MSCC's auxiliary vent stacks and SRU 30-meter stack. In 
addition to mass limits, the FIP establishes concentration limits on 
fuel burned in the units that vent to the auxiliary vent stacks and SRU 
30-meter stack. These concentration limits are 160 ppm H2S 
per 3-hour period and 100 ppm H2S per calendar day. When 
trigger events specified in the rule occur, MSCC must measure the 
H2S concentration in the fuel using length-of-stain detector 
tubes on a once-per-3-hour period.
    (7) The FIP establishes various recordkeeping and reporting 
requirements.
    It is important to note that, in cases where the provisions of the 
FIP address emissions activities differently or establish different 
requirements than provisions of the SIP, the provisions of the FIP take 
precedence. We also caution that if any of the four sources are subject 
to requirements under other provisions of the Act (e.g., section 111 or 
112, part C of title I, or SIP-approved permit programs under part A of 
title I), our promulgation of the FIP does not excuse any of the 
sources from meeting such requirements. Finally, our promulgation of 
the FIP does not imply any sort of applicability determination under 
other provisions of the Act (e.g., section 111 or 112, part C of title 
I, or SIP-approved permit programs under part A of title I).

II. Issues Raised by Commenters and EPA's Response

A. FIP Not Necessary

1. Ambient Data and Historical Modeling Show Attainment
    (a) Comment (CHS Inc., COPC, ExxonMobil, NPRA, MPA, MDEQ, MSCC, 
WETA): The FIP is not necessary for attainment of the NAAQS because 
ambient data show that the Billings/Laurel area has been for many years 
and continues to be in attainment with both the Federal and State 
SO2 ambient air quality standards for all averaging periods.
    Response: EPA does not agree that a FIP is not necessary because 
ambient data show attainment of the SO2 NAAQS. Ambient 
monitoring is limited in time and in space. Ambient monitoring can 
measure pollutant concentrations only as they occur; it cannot predict 
future concentrations when emission levels and meteorological 
conditions may differ from present conditions.
    EPA has long held that ambient monitoring data alone generally are 
not adequate for SO2 attainment demonstrations. 
Additionally, a small number of ambient SO2 monitors usually 
are not representative of the air quality for an area. (See reference 
document GGGGG, April 21, 1983, memorandum from Sheldon Meyers, 
Director, Office of Air Quality Planning and Standards (OAQPS), to 
Regional Air and Waste Division Directors, titled ``Section 107 
Designation Policy Summary,'' and reference document HHHHH, September 
4, 1992, memorandum from John Calcagni, Director, Air Quality 
Management Division, OAQPS, to Regional Air Division Directors, titled 
``Procedures for Processing Requests to Redesignate Areas to 
Attainment.'')
    Typically, modeling estimates of maximum ambient concentrations are 
based on a fairly infrequent combination of meteorological and source 
operating conditions. To capture such results on an ambient monitor 
would normally require a prohibitively large and expensive network. 
Therefore, dispersion modeling is generally necessary to 
comprehensively evaluate sources' impacts and to determine the areas of 
expected high concentrations. (Id.) Air quality modeling results would 
be especially important if sources were not emitting at their maximum 
level during the monitoring period or if the monitoring period did not 
coincide with potentially worst-case meteorological conditions. 
Further, ambient monitoring data are not adequate if sources are using 
stacks with actual heights greater than good engineering practice stack 
height (which indeed is the case with MSCC and ConocoPhillips) or other 
dispersion techniques for which SIP/FIP modeling credit is not allowed. 
(See also our discussion of related issues in our final action on the 
Billings/Laurel SO2 SIP (67 FR 22168, 22185-22187, May 2, 
2002.))
    Ambient monitoring data and air quality modeling data for a 
particular area can sometimes appear to conflict. This is primarily due 
to the fact that modeling results may predict maximum SO2 
concentration at receptors where no monitors are located.
    Moreover, our SIP Call for the Billings/Laurel area was based on 
modeled violations of the SO2 NAAQS, not monitored 
violations. (See reference documents Y and Z.) We took final action on 
the SIP Call in our May 2, 2002, action on the Billings/Laurel SIP (67 
FR 22168, 22173), and we are not revisiting it in this FIP action. It 
would be inconsistent and inappropriate to now rely solely on 
monitoring to determine necessary measures and demonstrate attainment.
    It is especially important to recognize that, as a result of our 
partial and limited disapproval of the Billings/

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Laurel SO2 SIP, we are legally obligated to promulgate a FIP 
for the area. See section 110(c)(1) of the CAA, 42 U.S.C. 7410(c)(1). 
However, the SIP deficiencies that triggered our partial and limited 
disapproval were varied and were not necessarily associated with 
problems that could be measured at an ambient monitor. For example, one 
basis for disapproval of the SIP was the State's use of improper (too 
tall) stack height credit for MSCC in modeling attainment of the NAAQS. 
In the real world, emissions at the actual (100 meter) height of the 
stack create less impact on monitored ambient concentrations in the 
Billings/Laurel area than if the emissions were emitted from a lower 
stack. Nonetheless, we had to partially disapprove the SIP due to the 
State's inappropriate grant of stack height credit, and section 110(c) 
of the CAA requires that we correct the deficiency. Since the State did 
not model attainment at the proper stack height credit for MSCC's 
stack, it was necessary that we do so and set emission limits for the 
stack consistent with our attainment demonstration. We believe MSCC has 
consistently been meeting the emission limits we are adopting, so there 
may be no reduction in actual emissions from the stack, but that does 
not mean the CAA allows us to forego this aspect of the FIP.
    Likewise, CAA sections 110(a)(2)(A) and (C) require that SIP 
control measures be enforceable. We disapproved several source 
monitoring methods because they were not adequate to determine 
compliance under all operating conditions. It may be impossible to 
measure the impact these SIP deficiencies may have on ambient 
SO2 concentrations in the area, but the CAA still requires 
that we correct the deficiencies. Regarding the emission limits and 
compliance determining methods for the flares, the State-only flare 
limits, which the State relied on to demonstrate attainment, may have 
positively impacted flare emissions in the past few years. However, the 
State did not include the State-only flare limits or adequate 
compliance determining methods in the SIP. Thus, the SIP remains 
deficient. We now have the responsibility to ensure that emission 
limits relied on to demonstrate attainment are included in the SIP and 
are practically enforceable, consistent with the requirements of 
section 110 of the Act.
    (b) Comment (MSCC, MDEQ): The State's SIP modeling, along with 
appropriate emission limits, show attainment of the NAAQS.
    Response: EPA addressed this issue in its actions on Montana's SIP 
submissions. As explained in those actions, EPA does not agree that the 
State's SIP modeling, along with appropriate emission limits, show 
attainment of the NAAQS. EPA's formal determinations regarding the 
attainment demonstration and emission limits were made in final actions 
on May 2, 2002 (67 FR 22168) and May 22, 2003 (68 FR 27908). The FIP 
fills the gaps for the provisions we disapproved.
    We note that we have not reopened our SIP actions as part of this 
action. Thus, to the extent the commenters are expressing their 
disagreement with EPA's actions on the SIP, their comments are not 
relevant to this action, and EPA is not re-considering them here.
    (c) Comment (ExxonMobil): EPA's proposed FIP ignores the 
substantial improvement in air quality in the Billings/Laurel area and 
instead predicts exceedances of NAAQS based upon modeling performed as 
long as 15 years ago. EPA's FIP proposal must be further examined in 
light of subsequent developments, including correct modeling and 
consideration of currently available information indicating compliance.
    Response: See response to comment II.A.1.(a), above, regarding 
ambient data and response to comments in section II.E., below, 
regarding modeling.
2. Existing Controls Sufficient
    (a) Comment (MDEQ, MSCC, COPC, ExxonMobil, MPA, NPRA, WETA): The 
FIP offers questionable improvements because the existing control plan 
provisions submitted by the state are adequate and contain sufficient 
SO2 emission controls and strategies and provide for the 
implementation, maintenance, and enforcement of the SO2 
NAAQS.
    Response: EPA addressed the adequacy of Montana's SIP submissions 
in its final actions on the SIP. As explained in those actions, EPA 
does not agree that the State's SIP control plan provisions are 
adequate and contain sufficient SO2 emission controls to 
show attainment of the NAAQS. EPA's formal determinations regarding the 
attainment demonstration and emission control plan were made in final 
actions on May 2, 2002 (67 FR 22168) and May 22, 2003 (68 FR 27908). In 
our May 2002 and May 2003 actions we disapproved various control plan 
provisions. The FIP fills the gaps for the provisions we disapproved. 
The FIP offers necessary improvements to the SIP by imposing new 
emission limits and reliable compliance determining methods to ensure 
attainment of the SO2 NAAQS.
    We note that we have not reopened our SIP actions as part of this 
action. Thus, to the extent the commenters are expressing their 
disagreement with EPA's actions on the SIP, their comments are not 
relevant to this action, and EPA is not re-considering them here.
    (b) Comment (CHS Inc., WETA, COPC, MDEQ, ExxonMobil, NPRA): In 
addition to the SIP, SO2 emissions in the Billings/Laurel 
area have decreased as a result of Consent Decrees and Montana Air 
Quality Permit changes. These limits are all federally enforceable 
because there are Title V operating permit conditions (CHS Inc.). EPA 
did not consider these emission reductions in making its determination 
that the FIP was necessary. The FIP proposal does not otherwise 
acknowledge the practical effects of the recent consent decrees between 
the primary refinery parties subject to regulation as well as other 
permitting actions that have occurred over the past eight years (MSCC, 
COPC).
    Response: EPA did not consider the emission reductions that 
resulted, or will result, from the consent decrees and/or State permit 
revisions to determine that the FIP was necessary or include the 
emission reductions in our modeling for several reasons.
    First, the FIP is required because we disapproved the SIP, and the 
State has not made revisions to the SIP to address the SIP's flaws. As 
noted in other responses, because we disapproved the SIP, we have a 
legal obligation to promulgate a FIP. See CAA section 110(c), 42 U.S.C. 
7410(c).
    Second, even though permits and consent decrees are federally 
enforceable, some permits can be revised without EPA approval and 
consent decrees have a limited lifespan.\2\ To protect the integrity of 
the attainment demonstration, and our statutory role in assessing SIP/
FIP adequacy, we believe that stationary source emission limits 
necessary to demonstrate attainment must be included in the FIP (or 
approved SIP). See, e.g., CAA sections 110(a)(2)(A), 110(i), 110(k)(3)-
(6), and 110(l), 42 U.S.C. 7410(a)(2)(A), (i), (k)(3)-(6), and (l). 
This ensures that changes to those limits will only be made with EPA's 
approval as a SIP or FIP revision,

[[Page 21422]]

following notice and comment rulemaking.
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    \2\ The State can revise construction permits without EPA 
approval, and, while EPA has authority to object to Title V permits, 
that authority is only available to ensure that underlying 
applicable requirements are included in the Title V permits. Thus, 
if those underlying requirements change, EPA may have no recourse at 
the Title V stage.
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    Third, the consent decrees and permitting actions, for some 
emission points, do not contain SO2 emission limits that are 
consistent with the averaging times of the SO2 NAAQS, 
specifically, the 3-hour and calendar day averaging periods. For 
example, the SIP establishes 3-hour, calendar day, and calendar year 
emission limits for CHS Inc.'s FCC regenerator/CO boiler stack. The 
January 17, 2007, final State construction permit (reference document 
IIIII) and the consent decree (reference document JJJJJ) indicate that 
the FCC regenerator stack SO2 emissions shall not exceed 50 
ppm by volume (corrected to 0% O2) for a 7-day rolling 
average [or a fresh feed of 0.3 percent by weight] and 25 ppm by volume 
(corrected to 0% O2) for a 365-day rolling average. None of 
the commenters has suggested these limits be converted to FIP mass 
limits that would apply over a 3-hour averaging period, and the State 
has not submitted a SIP revision with such limits.
    It should be noted that EPA did solicit comment on whether we 
should limit the main flares to 500 pounds of SO2 per 
calendar day. This value is consistent with the trigger point for 
certain analyses contained in settlements (i.e., consent decrees) 
between the United States and CHS Inc., ConocoPhillips, and ExxonMobil. 
We received limited comments on this proposal and have decided to keep 
the limit at 150 pounds of SO2 per 3-hour period to maintain 
consistency with the State's State-only limit.

B. EPA Exceeded Its Authority in Proposing a FIP

1. State's Responsibility
    (a) Comment (WETA, MPA, ExxonMobil): EPA's role is limited to 
determining whether or not a SIP is attaining and maintaining the 
NAAQS. Selecting the source mix and various control measures to achieve 
these ends has been determined by courts to be the sole responsibility 
of the state. EPA's proposed action intrudes on the primary 
responsibility of the state and local governments to implement the 
Clean Air Act (MSCC).
    Response: The commenters' characterization of EPA's role regarding 
SIPs is not accurate. We lack authority to question a state's choices 
of emissions limitations if they are part of a plan that satisfies the 
standards of the Clean Air Act. Train v. Natural Resources Defense 
Council, 95 S.Ct. 1470, 1481-1482 (1975). In our 2002 and 2003 actions, 
we found that Montana's SO2 SIP for Billings/Laurel did not 
fully satisfy CAA requirements. See 67 FR 22168, May 2, 2002 and 68 FR 
27908, May 22, 2003. Thus, pursuant to section 110(c) of the CAA, 42 
U.S.C. 7410(c), we are required to promulgate a FIP. In doing so, we 
stand in the state's shoes and have authority to determine emissions 
limitations and other measures for specific sources to fill gaps in the 
SIP. Central Arizona Water Conservation District v. EPA, 990 F.2d 1531, 
1541 (9th Cir. 1993); South Terminal Corp. v. EPA, 504 F.2d 646, 668 
(1st Cir. 1974) (citing previous version of CAA section 110(c)).
    We note that we have not reopened our SIP actions as part of this 
action. Thus, to the extent the commenters are expressing their 
disagreement with EPA's actions on the SIP, their comments are not 
relevant to this action, and EPA is not re-considering them here.
    (b) Comment (WETA): Since the State of Montana has already taken 
appropriate actions to reduce sulfur dioxide emissions, EPA does not 
have the authority under the CAA to adopt the proposed FIP.
    Response: See response to comment II.B.1.(a), above. The adequacy 
of the State of Montana's actions has already been considered by EPA in 
other rulemaking actions that addressed the State's SIP submission. 
Those actions are not the subject of EPA's present rulemaking, which 
promulgates the necessary measures to remedy the deficiencies EPA 
identified in its prior SIP reviews.
    (c) Comment (MSCC): States have primacy, and because EPA did not 
choose to exercise its rights in the comprehensive and competent state 
decision process, EPA may not default and then act.
    Response: Under section 110(c) of the Act, EPA is not required to 
participate in a state's administrative process before promulgating a 
FIP.
    (d) Comment (MSCC, MDEQ, ExxonMobil): EPA has no authority to 
question the wisdom of a state's choices of emission limitations if 
they are part of a plan that satisfies the standards of Sec.  110(a)(2) 
of the Act. As long as the ultimate effect of a state's choice of 
emission limitations is compliance with the NAAQS, the state is at 
liberty to adopt whatever mix of emission limitations it deems best 
suited to its particular situation. There is no evidence provided by 
EPA that Montana reached its material conclusions or choices in the SIP 
unreasonably. Additionally, EPA has not shown that additional controls 
beyond the SIP measures adopted by Montana are necessary to meet or 
assure SO2 NAAQS compliance.
    Response: See our responses to comments II.A.1.(a) and II.B.1.(a), 
above. Much of this comment pertains to our actions on Montana's SIP. 
We are not revisiting or reopening comment on those actions here. Our 
basis for finding that the SIP was not adequate to ensure attainment 
and meet other CAA requirements is described in our actions on the SIP. 
Once we disapprove part or all of a required SIP, section 110(c) of the 
Act requires that we issue a FIP. Our obligation in this action is to 
correct the SIP deficiencies we previously identified. Thus, the 
findings that triggered our responsibility to promulgate a FIP were 
established in the prior rulemaking actions reviewing Montana's SIP. 
EPA is not required to repeat those findings in the FIP rulemaking 
itself.
    (e) Comment (ExxonMobil): EPA cannot propose a FIP to replace a 
SIP, unless the SIP is substantially inadequate to ensure compliance 
with the CAA.
    Response: The commenter misstates the standard for promulgation of 
a FIP. Section 110(c) of the CAA is straightforward--a FIP is required 
if (1) EPA finds that a state has failed to make a required submission; 
(2) EPA finds that a plan submission does not satisfy the completeness 
criteria established under section 110(k)(1)(A) of the CAA; or (3) EPA 
disapproves a SIP in whole or in part. EPA partially disapproved the 
Billings/Laurel SO2 SIP; thus, a FIP is required. Contrary 
to the commenter's assertion, the obligation to promulgate a FIP is not 
contingent on an EPA finding of substantial inadequacy. As explained 
above, the findings triggering our responsibility to promulgate a FIP 
were made in the prior actions reviewing Montana's SIP.
    (f) Comment (MSCC): The commenter claims EPA's action violates the 
Tenth Amendment to the Constitution. The commenter also claims EPA's 
FIP is dictating the required controls in contravention of the holdings 
in Commonwealth of Virginia v. EPA, 108 F.3d 1397 (D.C. Cir. 1997) and 
Bethlehem Steel v. Gorsuch, 742 F.2d 1028 (7th Cir. 1984).
    Response: Our FIP compels no action on the part of the State and is 
not coercive vis-[agrave]-vis the State. Our FIP contains requirements 
applicable to four private companies. The Tenth Amendment is not 
implicated. Nor do our actions contravene Commonwealth of Virginia or 
Bethlehem Steel. The former case held that EPA cannot, in a SIP Call, 
dictate that a state adopt a particular control measure to

[[Page 21423]]

demonstrate attainment of the NAAQS. EPA had issued a SIP Call finding 
that the SIPs of 12 states were inadequate to meet the ozone NAAQS and 
in its SIP Call rule, specified that the states needed to submit SIPs 
that included the California Low Emission Vehicle Program. In this 
matter, we are promulgating a FIP, not issuing a SIP Call. We are not 
directing any action by the State. Thus, the Commonwealth of Virginia 
case is not relevant to our FIP. Bethlehem Steel is also not relevant 
to our FIP action. In that case, the 7th Circuit held that it was 
improper for EPA to partially approve an Indiana SIP revision so as to 
render it more stringent than the State intended. We are promulgating a 
FIP in this action, not acting on a SIP; thus, Bethlehem Steel does not 
apply. As we note elsewhere, once we disapprove a SIP, we are required 
to promulgate a FIP, and in promulgating the FIP, we stand in the 
state's shoes. See section 110(c) of the CAA, 42 U.S.C. 7410(c); 
Central Arizona Water Conservation District v. EPA, 990 F.2d 1531, 1541 
(9th Cir. 1993).
    (g) Comment (MSCC): The commenter argues that the cases EPA cited 
in the preamble to the proposed Billings/Laurel FIP, regarding its FIP 
authority, do not speak to the central question--``When and on what 
authority may the EPA undertake the draconian act of displacing a 
state's implementation plan?'' The commenter argues that the question 
is particularly sensitive in this case because the State and the 
sources spent years negotiating the SIP.
    Response: As noted in response to comment II.B.1.(e), the CAA 
requires that we promulgate a FIP whenever we disapprove a SIP, in 
whole or in part. While we are sensitive to the fact that the State and 
sources spent years negotiating the SIP, that does not change our 
obligation under the CAA.
2. No Adequate Basis for FIP
    (a) Comment (MSCC, ExxonMobil): Because EPA must find substantive 
noncompliance with some provision of the Clean Air Act, specifically, 
failure to attain NAAQS, and because that finding of substantial 
inadequacy must be clearly stated, the present FIP decision must fall. 
It is inadequate on both counts. EPA has not provided any evidence that 
the State plan is not working.
    Response: See our response to comment II.B.1.(e), above. The 
evidence supporting EPA's determinations regarding the adequacy of 
Montana's SIP is contained in the record for those rulemaking actions, 
and need not be repeated here. EPA's disapproval of the SIP triggered 
the obligation for a FIP. No separate showing that the State plan is 
not working or does not meet CAA requirements is needed as part of this 
action. Commenters' comments regarding EPA's SIP actions are not 
relevant for this rulemaking.
    (b) Comment (ExxonMobil): Even when the EPA has statutory authority 
for a particular rule, its technical decisions about the level of 
pollutant reduction needed to comply with the CAA and the control 
strategies necessary to meet the level of pollutant reduction must be 
rational. Courts ``confronted with important and seemingly plausible 
objections going to the heart of a key technical determination * * * '' 
will not presume that EPA would never behave irrationally. South 
Terminal Corporation v. Environmental Protection Agency, 504 F.2d 646, 
665 (1st Cir. 1974). In South Terminal Corporation, various interested 
parties challenged EPA's FIP on technical grounds. Id. at 662-66. The 
court held that EPA failed to adequately support its decision to 
promulgate the rules contained in the FIP and remanded the case to EPA 
to develop the record. Id. at 666. The court questioned EPA's position 
in light of contradictory modeling and data, concluding that ``it is 
not clear whether or not the ambient air at Logan meets, or will 
without controls by mid-1975 will meet, the national primary 
standard.'' Id. 664. Similarly, in the present FIP proposal, EPA has 
neither determined appropriate current modeling nor used currently 
available information.
    Response: The standards for judicial review of this rulemaking 
action are contained in section 307(d)(9) of the CAA, 42 U.S.C. 
7607(d)(9). We believe the emission limitations and other requirements 
in this FIP are reasonable and that the situation in the cited case is 
not analogous.\3\ The commenter has not identified any modeling that 
contradicts our attainment demonstration, which forms the basis for the 
FIP's emission limitations; nor has the commenter shown that a 
different model would result in substantially different emission 
limitations. Our responses pertaining to model selection and input data 
are contained in section II.E., below. Further, we note that it does 
not appear the commenter is suggesting that the entire SIP should be 
re-done based on more current modeling and more up-to-date information. 
On the contrary, the commenter seems satisfied with the EPA-approved 
emission limitations in the SIP,\4\ which were based on the very 
modeling that the commenter now claims is unreliable.
---------------------------------------------------------------------------

    \3\ In South Terminal Corporation, EPA had determined emissions 
reductions needed to achieve the ozone and carbon dioxide NAAQS 
based on monitored values that the Court found highly questionable 
(petitioners claimed the ozone monitor was defective). South 
Terminal Corporation, 504 F.2d 646, 662 (1974). The commenter seems 
to suggest that the Court rejected EPA's modeling approach, but in 
fact, the Court was satisfied with the rollback modeling that EPA 
used. Id.
    \4\ Among other things, the commenter asserts that the state SIP 
requirements are adequate to protect the NAAQS. See reference 
document YYYY, page 27.
---------------------------------------------------------------------------

    (c) Comment (ExxonMobil): Citing Hall v. United States 
Environmental Protection Agency, 273 F.3d 1146, 1159 (9th Cir. 2001), 
the commenter states that in acting on a SIP, the test EPA applies is 
to ``measure the existing level of pollution, compare it with the 
national standards, and determine the effect on this comparison of 
specified emission modifications.'' The commenter argues that in the 
FIP proposal, EPA did not correctly identify the existing level of 
pollution and ignored the substantial evidence of permanently reduced 
SO2 emissions and levels in the Billings/Laurel area. The 
commenter also argues that EPA's authority is limited by its mandate 
under the CAA to ensure attainment and maintenance of the NAAQS as well 
as the CAA's other general requirements.
    Response: See responses to comments II.A.1.(a), II.A.2(b), and 
II.E.1.(e) and (g). Also, the Hall case involved a challenge to EPA's 
approval of a SIP revision for Clark County, Nevada, and EPA's 
interpretation of section 110(l) of the CAA, which provides that EPA 
may not approve a SIP revision if it would interfere with attainment or 
other applicable requirements of the CAA. EPA asserted that its 
approval of the Clark County SIP revision was consistent with section 
110(l) because the revision did not relax the existing SIP. The Court 
disagreed, holding that 110(l) requires more--a determination that the 
specific revision, when considered in the context of the SIP elements 
already in place, can meet the Act's attainment requirements. Hall at 
1152, 1159. It was in these circumstances that the Court expected EPA 
to determine the extent of pollution reductions required and evaluate 
whether the reductions resulting from the revision would be sufficient 
to attain the NAAQS.
    In its reference to Hall, the commenter appears to be conflating 
two disparate concepts. The Hall Court was addressing EPA's action on a 
SIP revision and indicating that EPA was not adequately evaluating 
whether Clark County's rule change would interfere

[[Page 21424]]

with attainment and other CAA requirements. The Court was not 
establishing a standard for a FIP or indicating that EPA was requiring 
more than necessary for the area, which seems to be what the commenter 
is suggesting in the case of the Billings/Laurel FIP. As we explain in 
greater depth elsewhere in this notice, we are not starting from 
scratch with our FIP. Instead, we are working within the framework of 
the existing Billings/Laurel SIP to fill the gaps resulting from our 
partial and limited disapproval of discrete SIP elements. In this 
unique circumstance, where only discrete elements of the SIP were 
deficient, the CAA does not require us to reevaluate or replace the 
entire SIP or the basic modeling approach upon which it was based. 
Nothing in the CAA requires EPA to reject an entire SIP when only 
certain elements within it are not approvable, and doing so, where that 
is not necessary to address a discrete deficiency, would be 
inconsistent with the basic scheme of cooperative federalism embodied 
in the CAA.
    Nor are we required as part of this FIP to revisit our SIP Call or 
the bases for our SIP disapproval. Our task is to fix the portions of 
the SIP that were deficient. It is reasonable to continue to treat as 
valid the factors we found adequate to support the portions of the SIP 
we approved, and augment and/or replace those factors that we found 
inadequate. In fact, based on the holding in Train v. NRDC, 421 U.S. 57 
(1975), recited by this commenter and others, it would be inappropriate 
for EPA to now reject or replace the portions of the SIP that we 
approved as meeting the CAA's requirements, because to do so would be 
to intrude on the State's authority under the CAA to establish the mix 
of controls for the area.\5\ The State, of course, remains free to 
submit a SIP revision that reflects a different mix of controls across 
all the sources. This would be the mechanism, for example, whereby the 
State could adopt SIP limits that correlate to refinery consent decree 
limits.\6\ If the State were to submit such a revision, we would 
evaluate the revision according to the Act, our regulations, and the 
relevant cases.
---------------------------------------------------------------------------

    \5\ To the extent the commenter is arguing that we may do no 
more in this FIP than appears minimally necessary to attain the 
NAAQS, we reject that notion as well. See, e.g., Central Arizona 
Water Conservation District v. EPA, 990 F.2d 1531, 1541 (9th Cir. 
1993) (EPA ``stands in the shoes of the defaulting State, and all of 
the rights and duties that would otherwise fall to the State accrue 
instead to EPA.'') Under the CAA, states are not restricted to 
barely meeting the NAAQS. In fact, the opposite is true--states may 
exceed minimum requirements. See CAA section 116, 42 U.S.C. 7416. In 
any event, our modeled attainment demonstration resulted in 
projected values just at the 24-hour SO2 NAAQS (365 
[mu]g/m\3\) and just below the 3-hour SO2 NAAQS (1291.5 
[mu]g/m\3\). However, we think we had discretion to adopt limits (to 
replace those we disapproved) consistent with modeled ambient 
concentrations further below the NAAQS, if we had felt a larger 
margin of safety was justified to ensure attainment and maintenance.
    \6\ As we allude to in sections II.A.2.(b), II.D.4., and 
II.E.1.(e), the consent decree limits would need to be translated 
into limits that support an attainment demonstration for the 
SO2 NAAQS. In sections II.A.2.(b) and II.D.4., we 
identify some of our concerns with the consent decree limits.
---------------------------------------------------------------------------

    (d) Comment (ExxonMobil): EPA's proposal imposes costly technology 
requirements not rationally designed to achieving their stated 
objectives. While EPA has authority to impose an emission limitation, 
the emission limitation must be necessary to attain NAAQS. City of 
Santa Rosa v. EPA, 534 F.2d 150, 155 (9th Cir. 1976), vacated on other 
grounds, 429 U.S. 990 (1976). The EPA derived its authority in City of 
Santa Rosa from its statutory mandate to ensure compliance with NAAQS 
and the fact that no alternative to its proposal was adequate to ensure 
compliance with NAAQS. It is clear that Montana's existing SIP, 
supplemented as it is by further state and federally enforceable 
consent decrees are a more than adequate alternative.
    Response: The cited case actually stands for the proposition that 
EPA's authority to adopt measures to meet the NAAQS is expansive. EPA 
adopted a FIP provision that would have required a substantial 
reduction (up to 100%) in the supply of gasoline to major metropolitan 
areas in California, including Los Angeles. Even the EPA acknowledged 
that the rule would cause severe social and economic disruption, and 
the EPA Administrator at the time publicly advocated amendments to the 
CAA to provide relief from EPA's own FIP rule. Nonetheless, the Court 
held that economic and social disruption are not cognizable if (1) a 
measure is necessary to attain the NAAQS; (2) there is no statutory 
limitation on EPA's authority to adopt the measure; and (3) there are 
no equally effective, less burdensome alternatives. City of Santa Rosa 
at 151-154.
    The measures EPA is promulgating in this FIP are in no way 
comparable to the reduction in gasoline supply at issue in the City of 
Santa Rosa case. Our FIP is narrowly tailored to fill the gaps in the 
Billings/Laurel SIP. Section 110(c) requires us to promulgate the FIP. 
There is no statutory limitation on our authority to adopt the measures 
we are adopting. On the contrary, section 110(a)(2)(A) of the Act 
requires enforceable emission limitations as necessary or appropriate 
to meet the applicable requirements of the Act, which include 
attainment and maintenance of the SO2 NAAQS. Using ISC, the 
same model the State used to set the commenter's emission limits in the 
SIP, we have determined emission levels consistent with attainment and 
established corresponding emission limits on the flares, MSCC's main 
stack, and other emission units, whose emission limits we disapproved 
in our SIP action. While the authority to require monitoring, 
recordkeeping, and reporting requirements can be inferred from CAA 
sections 110(a)(2)(A) and (C), section 110(a)(2)(F) of the Act 
specifically indicates that the EPA Administrator may prescribe the 
installation, maintenance, and replacement of monitoring equipment by 
stationary sources, as well as reporting requirements. Our requirement 
for the refineries and MSCC to install monitoring equipment to measure 
flare gas flow and concentrations is consistent with this authority and 
is rationally related to the goals of the FIP, i.e., to ensure 
attainment and maintenance of the SO2 NAAQS. We do not 
believe estimating flare emissions or emissions from other units is a 
sufficient substitute for real-time monitoring for purposes of this 
FIP; estimation is not an equally effective technique.
    The commenter argues that the existing SIP and the State and 
federally enforceable consent decrees are a more than adequate 
alternative to our FIP requirements. This comment ignores the fact that 
we disapproved portions of the SIP as not meeting the CAA's 
requirements. Elsewhere we explain that the consent decree provisions 
are not sufficient to meet the CAA's requirements under section 110 
related to attainment and maintenance of the NAAQS. See, e.g., sections 
II.A.2.(b), II.D.4., and II.E.1.(e).
    (e) Comment (MSCC): EPA's failure to issue the FIP within the CAA's 
two-year deadline is important in this case. As a result of EPA's 
delay, EPA should have to consider the cleanup of emissions that has 
occurred and significant changes in modeling technology.
    Response: We regret that it has taken this long to issue the FIP. 
We disagree that missing the two-year deadline obviates our duty or the 
need for the FIP. The State has not submitted a SIP revision correcting 
the portions of the SIP that we disapproved, despite the passage of 
time. Regarding the argument that we should have considered the 
reduction in emissions since we disapproved the SIP, see our responses 
to comments in section II.A. In section II.E, we respond to comments 
arguing

[[Page 21425]]

that we should have used newer modeling technology.

C. Flare Monitoring

1. Flare Flow Monitoring
    (a) Comment (MSCC): The core flowmeter technology application for 
flare systems seems to be an established technology, with thousands of 
installations completed around the world on other types of gas and 
liquid streams. However, none was identified that is following the 
precise specifications of the FIP proposal. Installation and operation 
of a flow meter in flare gas service at MSCC are probably achievable 
today, but not at the flow range below 1 fps, and not with conventional 
QA/QC procedures. Flow monitors have a difficult time measuring or 
reliably detecting low flow velocities (under approximately 1.0 fps) 
without false positives or false negatives. EPA should revise the 
proposed rule that currently indicates:

``[t]he minimum detectable velocity of the flow monitoring device(s) 
shall be 0.1 feet per second (fps). The flow monitoring device(s) 
shall continuously measure the range of flow rates corresponding to 
velocities from 0.5 to 275 fps and have a manufacturer's specified 
accuracy of 5% over the range of 1 to 275 fps.
    The revised rule should read ``[t]he minimum resolution of the 
flow monitoring device(s) shall be 0.1 feet per second (fps) when 
measuring flow rates above 1.0 fps. The device(s) shall continuously 
measure the range of flow rates corresponding to velocities from 1.0 
to 275 fps and have a manufacturer's specified accuracy of 5% over the range of that range.''

    The rule should also clarify if ``accuracy'' is intended to be 5% 
of the full-scale range of the instrument (13.7 fps is 5% of 275 fps), 
or if this is intended to be 5% of the measured flow, which would be 
0.05 fps at a flow of 1 fps, and would clearly be non-achievable with a 
resolution of 0.1 fps.
    Response: EPA proposed the volumetric flow monitoring 
specifications based on what we saw was achievable in vendor literature 
(see reference documents NN and OO) and what was being required by 
regulation in the Bay Area Air Quality Management District (BAAQMD) 
(see reference document LL) and South Coast Air Quality Management 
District (SCAQMD) (see reference document CCC).
    The commenter asserts that installation and operation of a flow 
meter at the flow range below 1 fps are not achievable. However, 
various sources indicate that ultrasonic flow meters can measure in the 
range of 0.1 to 1 fps. For example, in ``Flare Gas Ultrasonic Flow 
Meter,'' J.W. Smalling, L.D. Brawsell, L.C. Lynnwoth and D. Russel 
Wallace, Proceedings Thirty-Ninth Annual Symposium on Instrumentation 
for the Process Industries, 1984, the authors reported ``initially, a 
modest objective was established to develop an ultrasonic flow switch 
capable of detecting leaks in flare lines corresponding to flow 
velocity on the orders of 0.3 ms/ (1 ft/s). As testing continued, 
however, it became apparent that the equipment could measure flows 
below 0.03 m/s (0.1ft/s) and up to at least 6 m/s (20 ft/s) in flare 
stacks * * *'' (see reference document KKKKK). See also reference 
document OO, ``the DigitalFlowGF868 meter achieves rangeability of 2750 
to 1. It measures velocities from 0.1 to 275 ft/s (0.03 to 85 m/s) in 
both directions, in steady or rapidly changing flow, in pipes from 3 
in. to 120 in. (76 mm to 3 m) in diameter.''
    Additionally, the BAAQMD (see reference document LL) and SCAQMD 
(see reference document CCC) require flow meters on flares. BAAQMD 
requires that the minimum detectable velocity shall be 0.1 fps and the 
SCAQMD requires monitors with a velocity range of 0.1 to 250 fps. Based 
on conversations with the BAAQMD, it appears that the refineries in the 
Bay Area have installed flow meters meeting the requirements of the 
rule (see reference document OOOOO).
    Based on the above, we conclude that flow meters are available that 
can measure in the velocity range below 1.0 fps, and other regulatory 
authorities are requiring such flow meters with success.
    The commenter also claims that installation and operation of a flow 
meter are probably not achievable with conventional QA/QC procedures. 
The QA/QC procedures are discussed below in response to comment 
II.C.1.(d).
    The commenter argues that flow monitors have a difficult time 
measuring or reliably detecting low flow velocities (under 
approximately 1.0 fps) without false positives or false negatives. As 
indicated in the response to comment II.C.1.(b) below, there are 
approaches available for improving measurement accuracy in the 0.1 to 
1.0 fps range. In addition, as the response to comment II.C.1.(b) 
indicates, in the final FIP we are specifying a separate accuracy range 
for the velocity range of 0.1 to 1 fps. Finally, we describe how we are 
addressing the false positive and false negative flows in response to 
comment II.C.1.(c).
    The commenter asked that the rule clarify if ``accuracy'' of the 
instrument is intended to be 5% of the full-scale range of the 
instrument or 5% of the measured flow. In the rule, we have clarified 
that ``accuracy'' of the instrument is the accuracy of the measured 
flow and not the ``full-scale range'' of the instrument.
    The commenter also suggests some changes to the rule. Apart from 
adding a separate accuracy range for the velocity range of 0.1 to 1 fps 
and clarifying that accuracy is based on the measured flow, we are not 
making any additional changes to this aspect of the rule. We explain 
our reasoning in the response to this comment II.C.1.(a) and in the 
responses to comments II.C.1.(b)-(d), below.
    (b) Comment (ExxonMobil, WSPA): Manufacturers of flow monitoring 
instrumentation publish impressive performance specifications regarding 
velocity measurement range and accuracy, but often manufacturers' 
claims are not actually achieved in practice over the long term. To 
achieve a high level of measurement performance in the field requires 
adequate lengths of straight flare header pipe upstream and downstream 
of the monitor, the absence of flow disturbances, etc. Where these 
criteria cannot be met, the advertised or predicted performance of the 
flow monitoring system may not be fully realized in practice. MSCC 
claimed that significant piping modifications and possible flare 
relocation would be required to provide such runs at accessible 
locations. CHS Inc. asserted that it is likely that the CHS refinery 
flare header will not have adequate distances of undisturbed piping for 
ideal installation. In this case, either major, costly piping 
modification will be required or the accuracy criteria will not be 
achievable.
    Response: The commenters are correct that piping modifications may 
be appropriate to optimize the measurements. Each flare system will 
have unique flow measurement location issues and will have to be 
addressed on a case-by-case basis. Sources may need to work with the 
flow monitor manufacturer and flow testers to assure that the monitors 
meet the FIP's specifications for accuracy and representativeness and 
manufacturer's requirements for assuring ongoing equipment performance.
    In addition to making piping modifications (e.g. flow 
straighteners), other approaches are available to improve the 
measurement accuracy in the 0.1 to 1.0 fps range. Among the approaches 
are the use of additional monitoring paths, monitoring paths of longer 
length, and unconventional monitor configurations and path locations. 
Another approach involves

[[Page 21426]]

the use of Computer Fluid Dynamics (CFD) for the existing piping. CFD 
analysis has been used to provide correction factors for a series of 
velocities across the range of flow velocities. For example, these 
factors have been used to correct flow measurement data for 
disturbances caused by upstream pipe irregularities. These approaches 
are discussed in ``A Total Approach to Flare Gas Flow Measurement for 
Environmental Compliance,'' Gordon Mackie, Jed Matson and Mike Scelzo, 
Institute of Measurement and Control--Environmental Conference 2006. 
(See reference document LLLLL.) (See also Note to Billings/Laurel 
SO2 FIP File regarding conversations with GE Sensing 
(reference document MMMMM)).
    Finally, to address concerns regarding the measurement accuracy in 
the 0.1 to 1.0 fps range, we are revising the rule to indicate that the 
flow monitor must have a manufacturer's specified accuracy of  20% over the range 0.1 to 1 fps. Based on conversations with a 
vendor, we believe this is achievable. The vendor indicated that they 
have provided methodologies for sources to meet the SCAQMD rule, which 
also requires 20% accuracy in the 0.1 to 1.0 fps range. Methodologies 
include a second interrogation path or straightening of pipe. (See 
reference document MMMMM.)
    (c) Comment (ExxonMobil, WSPA, NPRA, MSCC): Consistently achieving 
low flow detection limits can be very difficult. Spurious signal, 
resulting in ``eddy'' currents and back-and-forth flows in the flare 
header, can easily limit the detection and accuracy of low flow 
readings. Furthermore, sometimes a flow monitor will show an indication 
of flow even though water seals ahead of the flare stack remain intact 
(i.e., there is not flow to the flares). Other regulations in other 
jurisdictions allow the sources other means to positively determine 
when the flare is not operating (e.g., flare on/off monitoring device, 
pressure of water seal). ExxonMobil recommends that similar language be 
considered by the stakeholder process for inclusion in the EPA's 
proposed FIP, and thereby remove the uncertainty of low flow reading. 
MSCC claimed that the EPA proposed FIP language should be revised to 
allow flare operations to be monitored by other means, and to disregard 
low flow readings when the flare is not operating to eliminate falsely 
reported SO2 emissions, when in fact there are none.
    Response: We agree that it is appropriate to include in the 
regulation the ability to use other secondary means to determine 
whether flow is reaching the flare when the flow monitor indicates low 
flow. If the secondary device indicates that no flow is going to the 
flare, yet the continuous flow monitor is indicating flow, the 
presumption will be that no flow is going to the flare. We have revised 
the final rule to allow the use of flare water seal monitoring devices 
to determine whether there is flow going to the flare, in addition to 
the continuous flow monitoring device. See response to comment 
II.F.1.(a) regarding the comment seeking a s