[Federal Register: September 6, 2006 (Volume 71, Number 172)]
[Rules and Regulations]
[Page 52670-52698]
[DOCID:fr06se06-33]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R06-OAR-2005-TX-0018; FRL-8216-1]

Approval and Promulgation of Air Quality Implementation Plans;
Texas; Revisions to the Ozone Attainment Plan for the Houston/
Galveston/Brazoria Nonattainment Area

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: EPA is approving revisions to the Texas State Implementation
Plan (SIP) as it applies to the Houston/Galveston/Brazoria (HGB) ozone
nonattainment area. These SIP revisions result from more recent
information on ozone formation in the HGB area indicating that a
combination of controls on nitrogen oxides (NOX) and highly
reactive volatile organic compounds (HRVOCs) should be more effective
in reducing ozone than the measures in the previously approved 2001 HGB
attainment demonstration plan which relied almost exclusively on the
control of NOX. Approval of these revisions incorporates
these changes into the federally approved SIP.
    The approved revisions include a 1-hour ozone standard attainment
demonstration, motor vehicle emissions budgets, a demonstration that
all reasonably available control measures have been adopted for the HGB
area and revisions to satisfy the enforceable commitments contained in
the previously approved SIP. These revisions present a new mix of
controlled strategies in order to achieve attainment. These revisions
include changes to the industrial NOX rules, reducing the
stringency from a nominal 90 percent to 80 percent control and
revisions to the Texas Inspection and Maintenance (I/M) rules that drop
three counties from the I/M program.
    As part of the approved revisions to the HGB attainment
demonstration, Texas has adopted new control measures which EPA has
approved or is approving concurrent with this action. The new control
measures are increased control of HRVOC emissions and control of
emissions from portable gasoline containers. Also, in separate actions
in today's Federal Register, EPA is concurrently approving the
following emissions trading programs that relate to the HGB attainment
demonstration: revisions to the Mass Emissions Cap and Trade Program
for the HGB area, the Highly Reactive Volatile Organic Compound
Emissions Cap and Trade Program for the HGB area, the Emissions Credit
Banking and Trading Program, and the Discrete Emissions Credit Banking
and Trading Program.
    The SIP revisions to the HGB attainment demonstration addressed in
this rulemaking along with the HRVOC rules and emissions trading
programs being concurrently approved, will provide for timely
attainment of the 1-hour ozone standard in HGB as demonstrated through
the modeling analysis. Additionally, Texas has shown that these
revisions will not interfere with any applicable requirement concerning
attainment and reasonable further progress, or any other applicable
requirement of the Clean Air Act. (Section 110(l) demonstration).

DATES: This rule is effective on October 6, 2006.

ADDRESSES: EPA has established a docket for this action under Docket ID
No. EPA-R06-2005-TX-0018. All documents in the docket are listed on the
http://www.regulations.gov Web site. Although listed in the index, some

information is not publicly available, e.g., CBI or other information
whose disclosure is restricted by statute. Certain other material, such
as copyrighted material, is not placed on the Internet and will be
publicly available only in hard copy form. Publicly available docket
materials are available either electronically through
http://www.regulations.gov or in hard copy at the Air Planning Section (6PD-

L), Environmental Protection Agency, 1445 Ross Avenue, Suite 700,
Dallas, Texas 75202-2733. The file will be made available by
appointment for public inspection in the Region 6 FOIA Review Room
between the hours of 8:30 a.m. and 4:30 p.m. weekdays except for legal
holidays. Contact the person listed in the FOR FURTHER INFORMATION
CONTACT paragraph below or Mr. Bill Deese at<PHONE_NUMBER> to make an
appointment. If possible, please make the appointment at least two
working days in advance of your visit. There will be a 15 cent per page
fee for making photocopies of documents. On the day

of the visit, please check in at the EPA Region 6 reception area at
1445 Ross Avenue, Suite 700, Dallas, Texas.
    The State submittal, which is part of the EPA record, is also
available for public inspection at the State Air Agency listed below
during official business hours by appointment:
    Texas Commission on Environmental Quality, Office of Air Quality,
12124 Park 35 Circle, Austin, Texas 78753.

FOR FURTHER INFORMATION CONTACT: Erik Snyder, Air Planning Section
(6PD-L), Environmental Protection Agency, Region 6, 1445 Ross Avenue,
Suite 700, Dallas, Texas 75202-2733, telephone<PHONE_NUMBER>; fax number
214-665-7263; e-mail address<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, wherever ``we'',
``us'', or ``our'' is used, we mean the EPA.

Table of Contents

I. Final Action
    A. What Is The Background for This Action?
    B. What Action Is EPA Taking?
    C. What Other SIP Elements Did We Need To Take Final Action on
Before We Could Approve the Revised Attainment Demonstration?
II. What Revisions to State Implementation Plan Are Being Approved
Here or in Other Concurrent Actions?
    A. One Hour Ozone Attainment Demonstration
    B. New Control Measures
    C. Control Measures Have Been Revised or Repealed
    D. Reasonably Available Control Measures
    E. Section 110(l) Analysis
    F. Enforceable Commitments
    G. Motor Vehicle Emission Budgets
III. What Is EPA's Response to Comments Received on the October 5,
2005 Proposed Rulemaking for This Action?
    A. What Comments Were Received?
    B. Response to Comments on the Attainment Demonstration
IV. Statutory and Executive Order Reviews

I. Final Action

A. What Is the Background for This Action?

    On October 5, 2005, we proposed approval of the revisions to the
SIP as it applies to the HGB ozone nonattainment area (70 FR 58119).
The proposal provided a detailed description of these revisions and the
rationale for our proposed actions, together with a discussion of the
opportunity to comment. The proposed HGB attainment demonstration
revisions relies upon four separate actions that EPA proposed for
approval on October 5, 2005: Highly Reactive Volatile Organic Compound
Emissions Cap and Trade Program for the HGB Ozone Nonattainment Area
(70 FR 58138), Discrete Emission Credit Banking and Trading Program (70
FR 58154), Emissions Banking and Trading Revisions for the Mass
Emissions Cap and Trade Program for the HGB Ozone Nonattainment Area
(70 FR 58112), and a Emission Credit Banking and Trading Program (70 FR
58146). The public comment period for these proposed actions closed on
November 4, 2005. One adverse comment letter and one comment letter
supporting our action were received. The proposed SIP revision also
relies upon a separate action that EPA proposed for approval on April
7, 2005 (70 FR 17640) that included HRVOC rules requiring sources to
monitor and control HRVOCs. For more information, see the Technical
Support Documents or the proposal notices for the attainment
demonstration or the five other notices. This SIP revision also relies
upon a separate action that included measures controlling emissions
from portable gasoline containers that EPA approved on February 10,
2005 (70 FR 7041).
    The following submissions from Texas which requested revision of
the HGB SIP were considered for this action:
    January 28, 2003: This submission responded to the State's
settlement agreement to provide an accelerated evaluation of whether
the industrial NOX controls could be substituted with
controls on HRVOCs. Based on the study, the commission adopted rules
substituting controls on NOX emissions from industrial
sources with new controls on HRVOCs. Texas also adopted a number of
minor revisions to the general VOC rules. Finally, the State also
provided a demonstration that Texas Emission Reduction Program (TERP)
emission reductions would be sufficient to achieve 25 percent of the
NOX reductions needed to demonstrate attainment, i.e., about
14 tons per day (tpd).
    October 16, 2003: This submission delayed compliance for the I/M
program in Chambers, Liberty and Waller Counties. (Docket EPA-R06-OAR-
2005-TX-0035.)
    October 6, 2004: This submission repealed the I/M program in
Chambers, Liberty and Waller Counties. (Docket EPA-R06-OAR-2005-TX-
0035.)
    November 16, 2004: This submission repealed a ban on morning
operations of lawn service contractors.
    December 17, 2004: This submission met the State's commitment to
provide a mid-course review SIP. Based on the updated analysis, the
State further tightened controls on HRVOCs in Harris county and revised
or repealed a number of NOX control measures including, the
vehicle idling prohibition, the speed limit strategy, the voluntary
mobile emissions program and the commitment to achieve NOX
reductions beyond the initial 25 percent provided in January 2003
(i.e., revoked the State's enforceable commitment to achieve 42 tpd of
the NOX reductions that was included as part of the prior
attainment demonstration).

B. What Action Is EPA Taking?

    We are approving the following revisions to the 1-hour ozone
attainment plan for the HGB area:
     TCEQ's revised demonstration, submitted December 17, 2004,
that the 1-hour ozone standard will be achieved in 2007, as required by
the Texas State Implementation Plan, even though the ozone 1-hour NAAQS
was revoked in June 2005.
     The revised motor vehicle emissions budgets associated
with the revised attainment demonstration. The revised 2007 budgets are
89.99 tons per day (tpd) for volatile organic compound emissions and
186.13 tpd for NOX emissions.
     TCEQ's revised demonstration that all reasonably available
control measures have been adopted for the HGB area.
     Revisions to satisfy the enforceable commitments contained
in the previously approved SIP (November 14, 2001, 66 FR 57160). With
respect to its original enforceable commitment to reduce NOX
emissions, TCEQ has instead substituted reductions in HRVOCs for a
portion of these NOX reductions and shown that the HRVOC
reductions provide equivalent air quality benefits in reducing ozone
levels.
     Revisions to the industrial NOX rules submitted
January 28, 2003, which included several miscellaneous changes and the
reduction in stringency from a nominal 90 percent to 80 percent
control.
     Revisions to the Texas I/M rules that drop three counties
from the I/M program. In addition, several miscellaneous changes are
approved.
     Repeal of the vehicle idling rule.
     Repeal of the Small Spark Engine Operating Restrictions.
     Revisions to the Speed Limit Strategy.
     Revisions to the voluntary mobile emissions program.
    Our proposal to approve the revisions was published in the Federal
Register on October 5, 2005 (70 FR 58119). Table 1 lists the revised
elements of the HGB ozone SIP we are approving in this action.

  Table 1.--Revised Elements of the HGB Ozone SIP Being Approved by EPA
------------------------------------------------------------------------
                                 Date submitted
            Element                  to EPA              Comments
------------------------------------------------------------------------
1-hour standard attainment             12/17/04  Please see our proposed
 demonstration revisions.                         action and technical
                                                  support document for
                                                  more information.
Revised motor vehicle emissions        12/17/04  Revised budgets are
 budgets for 2007.                                89.99 tpd for volatile
                                                  organic compounds and
                                                  186.13 tpd for NOX.
Reasonably available control           12/17/04  Please see our proposed
 measures demonstration.                          action and technical
                                                  support document for
                                                  more information.
Revisions to satisfy the               12/17/04  Please see our proposed
 enforceable commitments                          action and technical
 contained int he previouisly                     support document for
 approved SIP (November 14,                       more information.
 2001, 66 FR 57160).
Revisions to the industrial NOX         1/28/03  Revisions to 30 TAC
 rules which included several                     Chapter 117, Sections
 misceallaneous changes and the                   117.10, 117.105-
 reduction in stringency from a                   117.108, 117.113-
 nominal 90% to 80% control.                      117.116, 117.119,
                                                  117.131, 117.135,
                                                  117.138, 117.141,
                                                  117.143, 117.149,
                                                  117.203, 117.205-
                                                  117.207, 117.213-
                                                  117.216, 117.219,
                                                  117.223, 117.301,
                                                  117.309, 117.311,
                                                  117.313, 117.319,
                                                  117.321, 117.401,
                                                  117.409, 117.411,
                                                  117.413, 117.419,
                                                  117.421, 117.463,
                                                  117.465, 117.473,
                                                  117.475, 117.478,
                                                  117.479, 117.510,
                                                  117.512, 117.520, and
                                                  117.534.
                                                 Repeal of 30 TAC
                                                  Chapter 117, Sections
                                                  117.104, 117.540, and
                                                  117.560.
Revisions to the Texas I/M              10/6/04  Revisions to 30 TAC
 rules that drop three counties                   Chapter 114,
 from the I/M program and make                    Sections114.1, 114.2,
 several misceallaneous changes.                  114.50, 114.52, and
                                                  114.53.
Repeal of the vehicle idling           12/17/04  Repeal of 30 TAC
 rule.                                            Chapter 114, Sections
                                                  114.500, 114.502,
                                                  114.507, and 114.509.
Repeal of the Small Spark              11/16/04  Repeal of 30 TAC
 Engine Operating Restrictions.                   Chapter 114, Sections
                                                  114.452 and 114.459.
Revisions to the voluntary             12/17/04  Please see our proposed
 mobile emissions program.                        action and technical
                                                  support document for
                                                  more information.
------------------------------------------------------------------------

    Texas has adopted a revised attainment demonstration that includes
the following new control measures:
     Hourly (short-term) limit and Annual Cap on HRVOC
emissions.
     Improved requirements for HRVOC Leak Detection and Repair
Program for fugitive emissions and flare monitoring.
     Requirements for portable gasoline containers. (EPA
approved February 10, 2005.)
    We approved the measure controlling emissions from portable
gasoline containers on February 10, 2005 (70 FR 7041). The SIP
revisions addressed in this rulemaking in conjunction with the new
HRVOC rules, will provide for timely attainment of the 1-hour ozone
NAAQS as demonstrated through the modeling analysis. In addition, Texas
has shown that these revisions will not interfere with any applicable
requirements concerning attainment and reasonable further progress, or
any other applicable requirement of the Clean Air Act, (Section
110(l)).

C. What Other SIP Elements Did We Need To Take Final Action on Before
We Could Approve the Revised Attainment Demonstration?

    In our proposed action we explained that we could not finalize
approval of the revised attainment demonstration for HGB until we
finalized approval of several related actions. These actions are
discussed below. In a separate rulemaking published in this issue of
the Federal Register we are approving the new measures to control HRVOC
emissions as part of the basis for this approval of revisions to the
HGB attainment SIP. In this action, when we refer to this program as
``the HRVOC rule'' or ``the HRVOC control program'', we are speaking of
the entire rule package entitled ``Control of Highly Reactive Volatile
Organic Compound Controls''. (Docket ID No. EPA-R06-OAR-2005-TX-0033.)
    The HRVOC rules were adopted by TCEQ based on recent findings that
certain highly reactive chemicals (ethylene, propylene, 1,3 butadiene
and butenes) contribute disproportionately to the ozone problem in the
HGB area. EPA previously issued a proposed approval of the HRVOC rules
on April 7, 2005 (70 FR 17640).
    In separate rulemakings published in today's Federal Register we
are approving additional measures related to the Revised 1-hour ozone
Attainment Demonstration for HGB. These rules include the HRVOC
Emissions Cap and Trade Program for the HGB ozone nonattainment area,
Discrete Emission Credit Banking and Trading Program (conditional
approval), Emissions Banking and Trading Revisions for the Mass
Emissions Cap and Trade Program for the HGB ozone nonattainment area,
and an Emissions Credit Banking and Trading Program. These actions are
further discussed in Section II.B. of this notice.

II. What Revisions to the State Implementation Plan Are Being Approved
Here or in Other Concurrent Actions?

A. One Hour Attainment Demonstration

    As required by the Clean Air Act, Texas has used photochemical grid
modeling in its demonstration that the control strategy for the HGB
area will achieve attainment of the 1-hour ozone NAAQS by 2007. Also,
as allowed for under EPA policy, TCEQ has introduced other evidence,
referred to as weight of evidence, to supplement the modeling analysis.
The modeling provided in the mid-course review SIP revision builds on
modeling performed for the January 2003 SIP revision which TCEQ
submitted in support of reducing the stringency of the industrial
NOX rules and adopting measures for the control of HRVOCs.
    This SIP revision actually relies on two sets of modeling analyses.
First, it relies on modeling performed by the TCEQ that is intended to
simulate the routine emissions that occur in the HGB area and determine
the level of routine emissions that can be allowed in the area yet
still provide for attainment. Second, the SIP relies on modeling that
was provided through a collaborative effort (known as project H13) of
the Houston Advanced Research Center, the TCEQ, the University of Texas
and the University of North Carolina. The project H13 report was
entitled,

``Variable Industrial VOC Emissions and Their Impact on Ozone Formation
in the Houston Galveston Area,'' April 16, 2004. This second modeling
effort was used to estimate the impact of non-routine emission events
on ozone levels. This two-pronged approach is consistent with
observations that indicate that Houston's air quality problems stem
from the combination of two phenomena, normal routine emissions and
large non-routine releases of HRVOC emissions. For a more complete
description of the modeling procedures and EPA's evaluation of these
procedures, see the Technical Support Document (TSD) in the Docket for
this action (RO6-OAR-2005-TX-0018) and the FR proposal notice October
5, 2005 (70 FR 58119).

B. New Control Measures

    TCEQ has adopted the following new control measures since the
previously approved SIP revision:
     Hourly (short-term) limit and Annual Cap on HRVOC
emissions.
     Improved requirements for HRVOC Leak Detection and Repair
Program for fugitive emissions and flare monitoring.
     Requirements for portable gasoline containers. (EPA
approved February 10, 2005).
1. Hourly (Short-Term) Limit and Annual Cap on HRVOC Emissions
    As discussed in the proposal notice (70 FR 58119) and Technical
Support Document (TSD), Texas relied primarily on two sets of modeling
in developing its control strategy. One set of modeling, performed by
TCEQ, is largely a traditional model formulation that examines the
routinely variable emissions which occur in the HGB area. Through this
modeling, TCEQ established that NOX emissions would not have
to be reduced as much as previously planned and routine emissions of
highly-reactive VOC emissions would have to be reduced. Through the
second set of modeling, examining the impact of large non-routine
releases of HRVOCs, it was established that the frequency and magnitude
of large non-routine releases of HRVOCs should also be reduced.
    Using both sets of modeling, TCEQ developed a key feature of the
HGB attainment strategy: Routine HRVOC emissions are targeted and
reduced through an annual cap-and-trade program, while the non-routine
emissions from emission events, maintenance, start-up and shutdown are
controlled through a short-term limit of 1200 lbs/hour. In a related
rulemaking in today's Federal Register, EPA is concurrently approving
the Highly-Reactive Volatile Organic Compound Emissions Cap and Trade
Program to control routine emissions of HRVOCs (see EPA-R06-OAR-2005-
TX-0033). Unique to the HGB attainment strategy, exceedances of the
short-term limit are not counted toward compliance with the annual cap
but are still subject to enforcement as a violation of the short-term
limit.
    Again, EPA recognizes that the approach of providing this partial
exclusion for emissions above the short-term limit is a departure from
practices in other cap and trade programs such as the acid rain program
and our guidance. We currently believe this approach is only warranted
in consideration of the Houston area's unique situation that combines
an extensive petrochemical complex and the availability of the
extensive data and analysis that were generated by the intensive ozone
study, TxAQS 2000 and in conjunction with a short-term limit.
Consideration of this novel approach is warranted in order to balance
the need to reduce both routine and upset emissions of HRVOC, but also
recognizes that large upset emissions are difficult to control in the
petrochemical industry and one significant event could result in a
facility consuming more than a month's emission allotment.
2. Improved Requirements for HRVOC Leak Detection and Repair Program
for Fugitive Emissions and Flare Monitoring
    TCEQ has implemented a number of new requirements for leak
detection and repair of components in HRVOC service. The changes
include, among other things, the following improvements:
     Inclusion of connectors in the program.
     Inclusion of other non-traditional potential leak sources
such as heat exchanger heads and man-way covers.
     Elimination of allowances for skipping leak detection
periods for valves.
     Requirements for third party audits to help insure that
effective leak surveys and repairs are conducted.
     Requirements that ``extraordinary'' efforts be used to
repair valves before putting them on the delay of repair list.
    For purposes of estimating emissions for compliance with the Short-
term and annual caps, TCEQ adopted rules requiring companies to assume
specific flare destruction efficiencies for properly operating flares
and for when a flare operates outside the parameters of 40 CFR 60.18.
EPA is approving the estimates used for flare destruction efficiency
for use in the attainment demonstration because the estimates are based
on the best information available. We, however, remain concerned about
the uncertainty created in the attainment demonstration by having a
significant source of emissions which cannot be directly measured.
    We note that some operating parameters for flares such as steam and
air assist ratios are not covered specifically by 40 CFR 60.18 but some
studies have indicated these parameters can impact flare efficiency.
Because of the prevalence of flares in the HGB area, we believe Texas
should strongly consider, for both flares in HRVOC service and general
VOC service, requirements for monitoring steam and air assist ratios to
insure that operators maintain these parameters, not covered by 40 CFR
60.18, in a range to insure optimum combustion. We also encourage TCEQ
to pursue new technology such as the Fourier Transform Infrared
Spectrophotometer which would eventually allow the direct measurement
of destruction efficiency in the field.
    For a full discussion of the improvements to these programs, see
the Proposal Notice and Technical Support Document for this action. EPA
is approving the emission reductions that have been projected for the
improved leak detection and repair rules. Our approval is based on the
improvements to the fugitive rule and Texas' commitment to perform a
rule effectiveness study and use improved emission inventory techniques
to estimate future emissions to confirm the effectiveness of the
program.
3. Requirements for Portable Gasoline Containers
    TCEQ has adopted standards for portable fuel containers sold in the
State which provide requirements to prevent leaks and spills. EPA
approved the TCEQ rules on February 10, 2005 (70 FR 7041). TCEQ
projected 2.9 tons/day of VOC emission reductions that are included in
the revised attainment demonstration modeling.

C. What Control Measures Have Been Revised or Repealed?

    Texas has revised a number of control strategies that were included
in the previously approved SIP. A brief description of the revisions
that EPA is approving follows. More details are provided in the
proposal notice (70 FR 58119) and Technical Support Document (TSD)
materials.
    Industrial NOX Controls: Texas revised its NOX rules to
reduce the controls from a nominal 90 percent control to 80 percent
control. We are approving the revisions to industrial NOX
controls in the HGB area.

    Vehicle Inspection and Maintenance Program in Three Rural Counties:
TCEQ has dropped the requirement for I/M in Waller, Liberty and
Chambers Counties. We are approving the removal of the I/M program in
these three counties.
    Removal of Small, Spark-Ignition Engine Operating Restrictions:
TCEQ has dropped this requirement which would have prohibited
commercial lawn services from operating during the morning hours. We
are approving the removal of these operating restrictions on small,
spark-ignition engines.
    Speed Limit Strategy from a 55 mph Maximum Speed Limit to a 5 Mile
Reduction in Speed Limits from Previous Levels: The Texas legislature
repealed TCEQ's authority to implement speed limits for environmental
purposes. Texas Department of Transportation had already reduced speeds
in the HGB area by 5 mph from 70 mph to 65 mph and from 65 to 60. These
reductions in speed limits of 5 mph remain in place, but the reductions
that would have been achieved by reducing speed limits on all roads
further to 55 mph will not be achieved.
    Removal of the Vehicle Idling Restriction: This measure that would
have prohibited prolonged idling of heavy duty diesel vehicles has been
repealed. We are approving the repeal of this rule.
    Revision to Delay the Compliance Date for Gas Fired Water Heaters
and Small Boilers: This rule is not being repealed, but its compliance
date has been delayed from December 31, 2004 to January 1, 2007. This
rule requires new water heaters sold in Texas to achieve lower
NOX emission rates.
    We are not approving changes to the rules for control of water
heaters at this time. It is a Statewide rule and the changes to the
rule impact other areas of the State and we have not yet analyzed the
above issues in areas of the State other than Houston. We note only
that the changes to the water heater rules do not impact the
approvability of the Houston mid-course review SIP revision.
    Revisions to the Voluntary Measures: Texas has revised the
voluntary mobile emissions program (VMEP) portion of the SIP. The VMEP
portion of the SIP that was approved in 2001, and was projected to
achieve 23 tpd of emissions reductions through various voluntary and
often innovative measures. TCEQ has recalculated the benefits as
yielding 7 tpd of NOX emission reductions. We are approving
the revisions to the VMEP.

D. Reasonably Available Control Measures

    A brief description of the Reasonably Available Control Measures
(RACM) revisions follows, for more details see the proposal notice (70
FR 58119) and Technical Support Document (TSD) materials.
    In EPA's November 14, 2001 notice approving the plan for the HGB
nonattainment area, EPA approved the analysis showing the plan was
implementing all Reasonably Available Control Measures. The
NOX reduction requirements of that plan were so substantial
no additional RACM measures could be identified in time for adoption as
a part of that plan and the State had to make an enforceable commitment
to adopt additional NOX measures which were expected to be
feasible in the near future. Now, based on the findings of the mid-
course review, Texas has determined that the NOX reductions
necessary for attainment, while still substantial, are not as great and
that control of HRVOCs is a more effective way of reducing ozone. Both
NOX and HRVOC controls, necessary for attainment, will be
fully implemented the last year of the strategy. In the last year of
the strategy, the point source controls alone will achieve an estimated
39 tpd of NOX reductions (based on review of the TCEQ's Mass
Cap-and-Trade Registry). Reductions in on- and off-road emissions will
also occur. Therefore, to advance attainment, additional reductions on
the order of 39 tpd would have to be achieved before the ozone season
of 2006. In Section 5.4 of the State Implementation Plan, Texas
explains why even with the repeal and revision of the measures, Texas
believes the RACM requirement is still being met. What follows is a
brief summary of EPA's evaluation of each of the revisions being
approved.
    Industrial NOX Controls: TCEQ has relaxed the
NOX rules for a number of NOX point source
categories. The original controls achieved a nominal 90% reduction in
point source emissions, with some categories reducing more than 90% and
some less than 90%. The new rules, being approved here today, achieve a
nominal 80% control. It is a convenient short hand to refer to the
control levels as 90% or 80% even though this does not accurately state
the level of reduction for individual source categories. TCEQ has
argued that the 90% controls would not advance attainment because the
current 80% control levels are scheduled to be implemented in 2007 and
it would not be reasonable to expect that a more stringent 90% control
could be implemented faster to advance attainment. EPA previously
agreed that the most expeditious schedule for the 90% controls would be
by 2007. EPA continues to believe that to be the case so that
implementation of 90% controls would not advance attainment. Even at
the 80% control level, the TCEQ rules are still similar in stringency
to the control levels implemented in California which have generally
been considered the most stringent in the country.
    Repeal of the I/M Program in 3 Rural Counties: Texas has chosen to
reduce the scope of its I/M program from eight counties to five
counties. The three counties that are being dropped are Chambers,
Liberty and Waller Counties which are the most rural counties in the
nonattainment area. The program was scheduled to be implemented in
2005. Using Mobile6, Texas has estimated that the program would achieve
0.87 tpd of emission reductions which is a smaller reduction estimate
than the Mobile 5 estimate included in the 2000 SIP and is less than
0.2% of the projected emissions for the area in 2007. Because of the
small amount of emission reductions, implementation of I/M in these
three counties would not be expected to advance attainment and
therefore should not be considered RACM.
    Removal of Small Spark Operating Restrictions: This measure would
prohibit lawn and garden service contractors for operation in the
morning hours from 6 am to 10 am. This measure was due to be
implemented in 2005. Texas decided that attainment could be reached
without the implementation of this measure. The measure was estimated
to achieve the equivalent of 7.7 tons/day of NOX emission
reductions. As such, its implementation would not advance the
attainment date. Therefore, EPA believes the morning lawn service ban
should not be considered a reasonably available control measure for the
HGB area.
    Speed Limit Strategy: The previously approved SIP provides for the
speed limits in the eight county area to be reduced to 55 mph. Later,
TCEQ decided to delay the implementation of the 55 mph until 2005, but
would implement speed limits that are 5 mph lower than the previous
speed limits, lowering 70 mph speed limits to 65 mph and 65 mph limits
to 60 mph starting in 2001. In the 2004 SIP revision, TCEQ decided to
make permanent the interim limits and forgo lowering the speed limits
to 55 mph. Based on Mobile6, lowering speeds all the way to 55 mph
would be expected to reduce emissions 2-3 tons/day. This is a lower
estimate

of emission reductions than predicted by Mobile5 in the 2000 SIP
revision. This small amount of emission reduction would not advance
attainment in the Houston area and therefore this measure is not
considered RACM.
    Vehicle Idling Restriction: Texas is dropping a rule that prohibits
idling of heavy duty vehicles for more than five minutes in the Houston
area. The measure was estimated to reduce NOX emissions by
0.48 tpd. Texas decided that attainment could be reached without the
implementation of this measure. This small amount of emission reduction
would not advance attainment for the area and therefore should not be
considered RACM.
    Delay in Compliance for the Water Heater Rule: In this case, TCEQ
still intends to implement the rule, but has delayed compliance until
2007. Since the adoption of the current rule, two American National
Standards Institute (ANSI) standards (the flammable vapor ignition
resistance standard and the lint, dirt, and oil standard); the United
States Department of Energy (DOE) energy efficiency standard; and the
EPA insulation foam ban have been implemented. The ANSI lint, dirt, and
oil standard and the flammable vapor ignition resistance standard were
effective on July 1, 2003, and were established for gas-fired water
heater safety reasons. The DOE energy efficiency standard was effective
on January 20, 2004. The EPA foam ban was effective on January 1, 2003,
and affects gas-fired water heaters, as water heater manufacturers have
historically used hydrochlorofluorocarbon as a blowing agent for
creating foam insulation. The implementation of these standards has
delayed the progression of the water heater technology and design.
Therefore, a design that meets the 10 ng/J emission limit in the Texas
rule will not be available for sale in the market by the January 1,
2005 compliance date.
    Because the new federal standards affect the design of new water
heaters and have made it impractical for the industry to meet Texas's
NOX limits for water heaters in a timely manner, EPA agrees
that this measure is being implemented as expeditiously as is
technically practicable. In other words, earlier implementation is not
technically practicable and therefore, since it would be infeasible, it
would not advance attainment.
    We have reviewed these changes in RACM that are summarized above
and discussed these changes in greater detail in our TSD. We are
approving these changes to RACM as part of the approval of this
attainment demonstration revision approval and determining that TCEQ
has satisfied the RACM requirements.

E. Section 110(l) Analysis

    A brief description of the 110(l) analysis follows, for more
details see the proposal notice (70 FR 58119) and Technical Support
Document (TSD) materials. Section 110(l) of the Clean Air Act says:

Each revision to an implementation plan submitted by a State under
this Act shall be adopted by such State after reasonable notice and
public hearing. The Administrator shall not approve a revision of a
plan if the revision would interfere with any applicable requirement
concerning attainment and reasonable further progress (as defined in
section 171), or any other applicable requirement of this Act.

    As previously discussed, Texas has developed a revised strategy
which relies on fewer reductions of NOX and more reductions
of VOC. Texas determined that the revisions will not interfere with
attainment or reasonable further progress or any other applicable
requirement under the Act and after careful review, EPA agrees. Texas
has completed the revised attainment demonstration with respect to the
1-hour standard which is being approved today. Attainment
demonstrations for the 8-hour standard are not required until June
2007.
    Prior to the time that attainment demonstrations are due for the 8-
hour ozone standard, it is unknown what suite of control measures a
State will choose to adopt for a given area to attain that standard.
During this period, to demonstrate no interference with the 8-hour
NAAQS, EPA believes it is appropriate to allow States to substitute
equivalent emission reductions (to compensate for control measures
being removed) which result in equal or greater air quality benefit
than those reductions being removed from the approved SIP. EPA believes
that preservation of the status quo in air quality during the time in
which new attainment demonstrations are being developed for the 8-hour
ozone NAAQS will prevent interference with the States' obligations to
develop timely attainment demonstrations and to attain as expeditiously
as practicable.
    To show that the compensating emission reductions are equivalent,
modeling or adequate analysis must be provided. The compensating
emission reductions must provide actual, new emission reductions
achieved in a contemporaneous time frame in order to preserve the
status quo. In addition, the emission reductions must be permanent,
enforceable, quantifiable, and surplus to be approved into the SIP. EPA
has determined that the revised HGB SIP has met each of these
requirements. See the proposal notice (70 FR 58119) and Technical
Support Document (TSD) materials.
    Contemporaneous: While contemporaneous is not defined in the Clean
Air Act, a reasonable interpretation is that the compensating control
measures be implemented within one year of the time frame for the
control measure being replaced. In this case, the new control measures
being used as substitutes are being implemented in virtually the same
time frames as the measures being replaced. The new measures have the
following compliance dates: tighter controls on HRVOC fugitive
emissions by March 31, 2004, monitoring for the HRVOC cap by 2005,
compliance with the HRVOC cap starting in 2006, and gas can rule
implementation in 2007. The measures being replaced, which are listed
previously in this notice, with the exception of the vehicle idling
ban, all had compliance dates in the approved SIP of 2005 or later. In
particular the largest emission reduction change by far, the difference
between 90 percent and 80 percent control on NOX, was not
scheduled to be fully realized until 2007. The enforceable commitment
measures only provided that the measures would be adopted by May 2004
and compliance would be achieved as expeditiously as possible but no
later than the beginning of the ozone season in 2007. Therefore, it can
be assumed the emission reductions from the NOX enforceable
commitments, had they been implemented, would not have occurred before
the 2005-2006 time frame, a time frame similar to that for the measures
to control HRVOCs which Texas has adopted a substitute. With regard to
the vehicle idling restrictions, the compliance date for this rule was
May of 2001. It was projected to achieve 0.48 tpd of NOX
emission reductions. It was discontinued effective December 23, 2004.
The improved HRVOC fugitive controls which began implementation in
March of 2004, more than offset the small reductions lost by the
discontinuation of the motor vehicle idling program after December 23,
2004.
    Equivalent: To demonstrate that the emission reductions were
equivalent, the TCEQ used the photochemical model to demonstrate that
the total collection of strategies in the current SIP revision is
equivalent or better in 8-hour ozone reduction effectiveness as
compared with the total collection of strategies in the SIP that was
approved in 2001, including the reductions that

would have occurred due to measures to meet the enforceable
commitments. Several 8-hour ozone metrics were calculated. EPA believes
that the new strategy and the old strategy are approximately equivalent
in 8-hour ozone benefit, with the new strategy slightly more effective
in reducing the peak ozone values and the old strategy slightly more
effective in reducing the predicted area of exceedances. Taking all of
the metrics into consideration and recognizing the uncertainties in the
modeling, we believe that Texas has demonstrated that the new strategy
is equivalent to the old strategy in 8-hour ozone benefit.
    Permanent: The emission reductions from the HRVOC rules are
permanent as sources will have to maintain compliance with new measures
indefinitely.
    Enforceable: EPA has reviewed the enforceability of the substitute
measures in separate rules.
    The Portable Fuel Container Rule was approved: February 10, 2005,
70 FR 7041. EPA is also approving concurrently in a separate notice the
fugitive emission controls and improved monitoring requirements for
HRVOCs (proposal on April 7, 2005, 70 FR 17640). Finally, concurrent
with this Federal Register notice EPA is approving the HECT program. In
each of these rulemakings, EPA has evaluated whether the substitute
rules are enforceable, considering such issues as whether the rules
have adequate test methods, monitoring requirements, record keeping
requirements and whether the State has adequate enforcement authority
to ensure the limits are achieved. By our approval elsewhere in the
Federal Register today, these substitute rules are federally
enforceable and enforceable by the public through citizen suit.
    In summary, we believe the substitute measures result in equivalent
8-hour benefit and that the new measures are contemporaneous,
enforceable and permanent. Therefore, we believe approval of these
revisions to the approved SIP will not interfere with attainment of the
8-hour standard.
    The 1-hour standard was revoked on June 15, 2005 for the HGB area.
The approved SIP, however, committed the State to adopt control
measures of 56 tpd of NOX, unless the State could show that
these NOX reductions were not needed for attainment of the
1-hour standard. We have discussed elsewhere in this notice (and in the
proposal and TSD), EPA's evaluation of the revised 1-hour attainment
demonstration and are approving these revisions.
    Texas submitted, and EPA has approved, revisions to the rate of
progress (ROP) plan (February 14, 2005, 70 FR 7407) based on the
revised strategy. These revisions will ensure that 1-hour ROP is met
for each three year period out to the 1-hour attainment date of
November 15, 2007.
    Other than for ozone, the HGB area currently meets all other
National Ambient Air Quality Standards. The plan revisions being
considered would not be expected to impact compliance with the CO,
SO2 or Lead NAAQS as these pollutants are not affected by
these rules.
    The revisions to the NOX rules do affect emissions of
NO2 and thus could potentially impact attainment with the
NO2 standard. The HGB area, however, meets the
NO2 standard at today's level of NO2 emissions
and the revised plan will reduce NO2 emissions dramatically
from existing levels and thus will not interfere with maintenance of
the NO2 standard.
    Similarly, the HGB area currently meets the NAAQS for
PM2.5. NOX and VOCs are precursors to the
formation of PM2.5. Although the revised plan does not
reduce NOX emissions as much as the previous attainment
demonstration SIP revision approved by EPA in November 2001, the
revised plan will result in additional NOX and VOC
reductions beyond today's levels (emission levels at the time of this
notice). Therefore, the revised plan will not interfere with the
continued attainment of the PM2.5 standard.
    Section 110(l) applies to all requirements of the Clean Air Act.
Below are requirements potentially affected by TCEQ's rule change and a
brief discussion of EPA's analysis.
    Reasonably Available Control Technology (RACT) requirements: EPA
has previously approved the NOX and VOC rules in the HGB
area as meeting the CAA's RACT requirements. The revised NOX
rules remain substantially more stringent than the previously approved
RACT requirements. The new HRVOC rules build on the previously approved
RACT requirements. In addition, these revisions do not impact the major
sources applicability cutoffs. Therefore, these revisions do not
interfere with the implementation of RACT.
    Inspection and maintenance programs (I/M): This revision drops
three counties from the I/M program. These counties are not included in
the urbanized area as defined by the Census Bureau. Thus, I/M is not
required to be implemented in these counties and these revisions do not
interfere with meeting the I/M requirements of the CAA.
    Air Toxics: There are no Federal ambient standards for air toxics
and these rules do not interfere with implementation of any federal
MACT standards, therefore, these rule revisions do not interfere with
compliance with any air toxics standards under sections 112 or 129 of
the CAA. We note that air toxic levels of butadiene and formaldehyde
are expected to decrease as a result of the revised plan, because the
HRVOC rules directly regulate emissions of butadiene and ethylene.
Formaldehyde is formed from ethylene in the photochemical reactions
leading to ozone.

F. Enforceable Commitments

    In the SIP approved in November 2001, there were enforceable
commitments to achieve additional NOX reductions and
enforceable commitments to incorporate the latest information into the
SIP. This section contains a brief summary of the enforceable
commitments which were approved in the November 2001 Federal Register
and a short discussion of how they were met or are being revised.
    Commitment: To perform a mid-course review (including evaluation of
all modeling, inventory data, and other tools and assumptions used to
develop this attainment demonstration) and to submit a mid-course
review SIP revision, with recommended mid-course corrective actions, to
the EPA by May 1, 2004.
    Discussion: Texas provided, in the December 2004 submission, a mid-
course review that included new modeling with new more recent episodes
(including updated emissions) based on the Texas 2000 study. The State
submitted control measures that, based on the demonstration, will
result in attainment of the 1-hour standard as expeditiously as
practicable. Therefore, EPA believes the commitment for a mid course
review has been satisfied.
    Commitment: To perform new mobile source modeling for the HG area,
using Mobile6, EPA's on-road mobile emissions factor computer model,
within 24 months of the model's release.
    Discussion: The mid-course review modeling employed Mobile6 for the
on-road mobile source inputs satisfying this commitment.
    Commitment: If a transportation conformity analysis is to be
performed between 12 months and 24 months after the Mobile6 release,
transportation conformity will not be determined until Texas submits an
MVEB which is developed using MOBILE6 and which we find adequate.
    Discussion: This commitment was not applicable because
transportation

conformity was not performed during the time period.
    Commitment: To adopt rules that achieve at least the additional 56
tpd of NOX emission reductions that are needed for the area
to show attainment of the 1-hour ozone standard, including the adoption
of measures to achieve 25% (14 tpd) of the needed additional reductions
(56 tpd), and to submit those adopted measures to EPA as a SIP revision
by December 2002. To adopt measures for the remaining needed additional
reductions and submit these adopted measures to EPA as a SIP revision
by May 1, 2004.
    Discussion: In the January 28, 2003 submission, TCEQ provided the
demonstration that the TERP program meets EPA's requirements as an
economic incentive program and will achieve the required 14 tons/day of
emissions reductions. EPA has approved the TERP program in a separate
Federal Register action which discusses how the TERP program meets the
EIP requirements (August 19, 2005, 70 FR 48647). Through the attainment
year of 2007, 38.8 tons/day of emission reductions are projected for
the TERP program based on a $5,000/ton cost effectiveness. The total
obligation for emission reductions from TERP is 32.9 tpd. TERP
originally replaced two measures: a morning construction ban (6.7 tpd
NOX equivalent) and accelerated introduction of Tier II/III
equipment (12.2 tpd). After allocating 18.9 tpd from TERP to replace
these two measures, the program still is projected to produce an
additional 19.9 tpd of reductions which is sufficient to provide the
additional 14 tpd of emissions reductions needed to meet the
enforceable commitment. Thus, EPA believes the enforceable commitment
to achieve 25% of the 56 tpd of NOX reductions has been
satisfied.
    We note two developments with the program. The average cost
effectiveness of TERP projects, to date, is $5500/ton and the Texas
legislature moved to cut some of the funding for the program in the
last session. TCEQ may have to shift some of the TERP funding from
other areas such as Corpus Christi or Victoria, which currently meet
the 8-hour ozone standard, to the HGB area to insure that the emission
reduction targets are met.
    For the rest of the enforceable commitments to adopt and submit
rules to achieve the remaining 42 tpd NOX reductions due by
May 1, 2004, Texas determined that these additional NOX
reductions would not be necessary for the area to attain. Instead, as
discussed elsewhere in this document and the proposed approval notice
(70 FR 58119), TCEQ has instead adopted and has begun implementing a
strategy to reduce emissions of HRVOCs. EPA believes that the new
strategy will attain the one-hour standard. This is further discussed
in other sections of this notice, the proposal notice, and the TSD.
    Commitment: That the rules will be adopted as expeditiously as
practicable and the compliance dates will be expeditious.
    Discussion: TCEQ adopted its measures for the control of HRVOC
first in 2002 and has revised them three times since then. The
compliance dates in the rules are based on the need to develop
monitoring plans, quality assurance/quality control programs, install
the monitors, and develop control plans based on the monitoring
results. EPA believes that the implementation of these new measures is
as expeditious as practicable.
    Commitment: That the State would concurrently revise the Motor
Vehicle Emissions Budgets (MVEBs) and submit as a revision to the
attainment SIP if additional control measures reduce on-road motor
vehicle emissions. Texas stated that measures which could limit future
highway construction, such as growth restrictions, may not be included.
    Discussion: Texas has revised the mobile source budget to account
for TERP reductions and other adjustments to the mobile source
emissions estimates.
    Summary: Based on the above analysis, we have determined that TCEQ
has satisfied the requirements of the enforceable commitments contained
in the approved Houston/Galveston SIP.

G. Motor Vehicle Emissions Budgets

    The MVEBs established by this plan and that EPA is approving are
contained in Table 2. The development of the MVEBs are discussed in
section 3.5 of the SIP and were reviewed in the TSD. We are approving
the new MVEB because we find the budget to be consistent with the
attainment plan.

     Table 2.--2007 Attainment Year Motor Vehicle Emissions Budgets
                             [Tons per day]
------------------------------------------------------------------------
                          Pollutant                               2007
------------------------------------------------------------------------
VOC..........................................................      89.99
NOX..........................................................     186.13
------------------------------------------------------------------------

III. What Is EPA's Response to Comments Received on the October 5, 2005
Proposed Rulemaking for This Action?

A. What Comments Were Received?

    The following comment letters were received on the October 5, 2005
proposal:
    (1) November 4, 2005 letter from John D. Wilson, Executive Director
of Galveston-Houston Association for Smog Prevention for the Galveston-
Houston Association for Smog Prevention, Environmental Defense (Texas
Office), Lone Star Chapter of the Sierra Club, and Public Citizen
(Texas Office). Comments from this group will be referred to as
``(Wilson)''.
    (2) November 4, 2005 letter from Matthew L. Kuryla of Baker Botts
LLP on behalf of BCCA Appeal Group. Comments from this group will be
referred to as ``commenter (BCCAAG)''. Commenter BCCAAG included a list
of BCCA Appeal Group members as follows: Air Products, L.P.; Dynegy,
Inc.; Entergy Gulf States, Inc.; Enterprise Products Operating, L.P.;
Exxon Mobil Corporation; Greater Fort Bend Economic Development
Council; Lyondell Chemical Company; Reliant Energy, Inc.; Shell Oil
Company; Texas Genco; Texas Instruments Incorporated; Texas
Petrochemicals, L.P.; and Valero Refining-Texas, L.P.

B. Response to Comments on Attainment Demonstration

    In general the commenter (BCCAAG) indicated that they support
approval of the proposed attainment demonstration revisions and did not
have any adverse comments on this SIP revision. They indicated that the
revisions represent the most effective, technically and scientifically
robust plan yet advanced for achieving air quality goals in the HGB
airshed and the revised control strategy will bring the area into
attainment. They continued by indicating that the revised plan is
already reducing the number of days that ozone exceedances occur and
the magnitude of the high and second high ozone value at regulatory
monitors has decreased substantially in the last three years. Commenter
(BCCAAG) supported the proposed approval indicating that the revised
plan did meet RACM and the revised control strategy would reach
attainment.
1. General Comments
    Comment GC1: A commenter (Wilson) indicated that the proposed plan
fails to adequately demonstrate that its implementation, maintenance,
and enforcement will lead to attainment of

the 1-hour national air ambient quality standards (NAAQS) for ozone in
the Houston-Galveston-Brazoria (HGB) area. State ambient monitoring
results show that the HGB area already has failed the test for
attainment of the 1-hour ozone standard by the statutory deadline of
November 15, 2007, further demonstrating that the SIP revision is
``substantially inadequate to attain'' the ozone NAAQS by the deadline
established in the Clean Air Act (CAA). Thus, as demonstrated in these
comments, the EPA Administrator must find that:
     Texas has failed to satisfy the minimum criteria under
section 110(k); \1\ and
---------------------------------------------------------------------------

    \1\ 42 U.S.C. 7509(a)(1) and (2).
---------------------------------------------------------------------------

     The plan is substantially inadequate.
Then, based on these findings, the Administrator must require that the
TCEQ submit a revised plan demonstrating attainment within no more than
18 months.\2\
---------------------------------------------------------------------------

    \2\ 42 U.S.C. 110(k)(5).
---------------------------------------------------------------------------

    Commenter (Wilson) also urged EPA to disapprove the attainment plan
because they believe the plan does not include complete modeling,
enforceable versions of all Reasonably Available Control Measures
(RACM) and a control strategy sufficient to achieve attainment. The
commenter (Wilson) went on to say because they believe the plan should
be disapproved, EPA must commence promulgation of a Federal
Implementation Plan (FIP).
    Response GC1: In the following responses, we address the specific
concerns raised by the adverse comments in more detail. We believe the
revised plan provided by the State of Texas is fully approvable under
the Act, as we have documented in this notice and will provide for
attainment as expeditiously as practicable which is by November 15,
2007, and that the revised plan includes all reasonably available
control measures. Therefore, we are finalizing our approval in this
action. Furthermore, because we are fully approving the plan as meeting
the requirements of 182(c)(2) and (d) of the Act, it is unnecessary to
commence development of a FIP.
    Comment GC2: Commenter (Wilson) indicated TCEQ has not provided
modeling that shows attainment by 2007. The commenter also indicated
that six monitors in the area have already had four to six exceedances
of the 1-hour ozone NAAQS and the area has already failed to attain by
November 17, 2007 based on monitoring data for 2005. The commenter also
contended that two one-year extensions are specifically restricted to
the dates listed in Table 1 of Section 7511(a)(1), and that they do not
apply to the Severe-17 area deadlines set in Section 7511(a)(2).
Therefore, the commenter argues, these extensions cannot change the
attainment date of Severe-17 areas such as Houston. The commenter also
states that there is no demonstration of maintenance of the ozone
standard below the 0.12 ppm one-hour standard beyond 2007.
    Response GC2: EPA has taken the position that for nonattainment
areas subject to the requirements of subpart 2 of Part D of the Act,
the area needs to demonstrate that in the attainment year, the area
will have air quality such that the area could be eligible for the two
one-year extensions provided under Section 181(a)(5) of the Act. See 66
FR 57160, 57163-64 (November 14, 2001). EPA disagrees that Severe-17
areas such as Houston are not entitled to the extensions provided in
Section181(a)(5). It is our interpretation that the Severe category in
Table 1 of Section 181(a)(1) encompasses both Severe-17 and Severe-15
areas. Table 1 sets an attainment date of 15 years for severe areas
with a 1988 ozone design value between .180 and .280 ppm. However,
Section 181(a)(2) of the Act modifies Table 1 to provide an attainment
date of 17 years for severe areas with a design value of between .190
and .280 (``Severe-17 areas''). For those areas with a design value
above .190, Congress plainly intended to allow two years longer to
attain than the remainder of the severe areas included in Table 1.
Table 1 in Section 181(a)(1) cannot be read in isolation, and must be
read in conjunction with Section 181(a)(2). EPA thus interprets Section
181(a)(5) as providing for attainment date extensions for all severe
areas, including those whose attainment date in Table 1 is modified by
Section 181(a)(2).
    EPA interprets Section 181(a)(2) as simply recognizing that Severe
areas with a higher design value will need additional time to reach
attainment and thus is simply extending the date in Table 1 for severe
areas with high design values. There is nothing in Section 181 that
directly excludes Severe-17 areas from the extensions provided for in
Section181(a)(5). The commenter seems to suggest that even though
Congress recognized that Severe-17 areas would need more time to reach
attainment, they are not entitled to the extensions in Section
181(a)(5). This interpretation would result in the Severe-17 areas
getting no more time to attain than Severe-15 areas that potentially
could qualify for the two one-year extensions. This would be an absurd
result. Under the commenter's interpretation, all areas, including
those designated ``Extreme'', would be entitled to attainment date
extensions, with the sole exception of Severe-17 areas. This would mean
that severe areas with design values under .190 would be allowed two
one-year extensions, providing them with an attainment period of up to
17 years, while the Severe-17 areas, which were intended to have two
years longer to attain than the other severe areas, would be held to
their initial 17-year attainment period, thereby eliminating the very
distinction between the areas that Congress intended in section
181(a)(2). The better reading is that Severe-17 areas should be
eligible for the 2 one-year extensions (if they qualify for them)
provided for in Section181(a)(5). EPA has consistently taken this
position. Indeed, in the approval of the full attainment demonstration
SIP for the Houston area in our November 14, 2001 (66 CFR 57160,
57163), we indicated in a response to a comment (that the modeling
should show attainment in 2005) that EPA's modeling guidance provided
for modeling to demonstrate attainment in the last year (2007 in this
case) such that it would be eligible or clean data extensions in
accordance with Section 181(a)(5). It has been EPA's opinion at least
since 2001 that Houston, a Severe-17 area, was entitled to the
extensions in question. If the commenter's interpretation was applied
(interpret 181(a)(5) as not applying to Severe-17 areas), three years
of data (2005-7) would be needed to yield attainment in 2007 and to
yield those monitor levels, EPA would have had to modify modeling
guidance and required TCEQ to model 2005 future year for Houston and
show no exceedances in the SIP revisions EPA approved in 2001. Once
again, if the commenter's assertion were correct, Severe-17 areas would
not be eligible for clean data extensions with the end result being an
attainment date not much different than if the area had been designated
a Severe-15 area.
    In addition, under EPA's interpretation, a Severe-17 area does not
automatically get the extensions. They have to demonstrate significant
progress towards attainment. Nonattainment areas subject to the
requirements of subpart 2 of part D of the Act, need to demonstrate
that in the attainment year, the area will have air quality such that
the area could be eligible for the two one-year extensions provided
under section 181(a)(5) of the Act. Under section 181(a)(5), an area
that does not have three years of data demonstrating

attainment of the ozone NAAQS, but has complied with all of the
statutory requirements and that has no more than one exceedance of the
NAAQS in the attainment year, may receive a one-year extension of its
attainment date. Assuming those conditions are met the following year,
the area may receive an additional one-year extension. If the area has
no more than one exceedance in this final extension year, then it will
have three-years of data indicating that it has attained the ozone
NAAQS. There is no reason to believe that Congress did not intend for
Severe-17 areas to exercise this option.
    Moreover, EPA believes this approach is consistent with the
statutory structure of subpart 2. Under subpart 2, many of the planning
obligations for areas were not required to be implemented until the
attainment year. Thus, Congress did not assume that all measures needed
to attain the standard would be implemented three years prior to the
area's attainment date. For example, areas classified as marginal--
which had an attainment date of three years following enactment of the
1990 Clean Air Act Amendments--were required to adopt and implement
RACT and I/M ``fix-ups'' that clearly could not be implemented three
years prior to their attainment date. Similarly, moderate areas were
required to implement RACT by May 1995, only 18 months prior to their
attainment date of November 1996. Also, the ROP requirement for
moderate and above areas, including the 15% plan for reductions by
November 1996, applies through the attainment year. Thus, EPA believes
that Congress did not intend that these additional mandatory reductions
be in excess of what is needed to achieve three years of ``clean
data.'' EPA does not require areas to demonstrate that the area will
have three years of data (2005-2007) showing attainment in the
attainment year. However, EPA does believe that the Act requires and
that it is prudent for States to implement controls as expeditiously as
practicable. As discussed elsewhere in this notice, additional
reductions are being made in the Houston area after the 2005 ozone
season, so it is still possible for the additional measures to result
in the area reaching attainment by 2007. For these reasons, EPA does
not agree with the commenter that the State's attainment demonstration
is inadequate because of the exceedances that occurred at six monitors
in 2005.
    A plan for maintenance of the NAAQS is not necessary for the
attainment demonstration to be approved. A State is not required by the
Act to provide a maintenance plan until the State petitions for an area
to be redesignated to attainment. While it is not necessary for the
State to provide for maintenance of the standard at this time, we do
believe emissions in the HGB area will continue to decrease after 2007
due to on- and off-road vehicle emission control programs that will
provide additional reductions as the fleet continues to turnover after
2007. TCEQ is also required to provide an 8-hour ozone attainment SIP
for the HGB area that will likely require a new mixture of control
measures to demonstrate future attainment of the 8-hour ozone standard.
So there is reason to believe that air quality will continue to improve
after the 1-hour attainment date.
    Comment GC3: Commenter (Wilson) suggested the plan should address
other air pollution concerns such as reasonable further progress of the
8-hour standard in addition to attainment of the one-hour standard. The
commenter suggested the plan should provide as much progress as
possible toward implementing the 8-hour standard as the requirements of
the Act and EPA's implementing regulations allow.
    Response GC3: EPA established submission dates for 8-hour SIPS in
its Phase 2 ozone implementation rule (70 FR 71611). SIPs addressing
reasonable further progress and attainment of the 8-hour standard are
due in 2007 and are not the subject of this rulemaking. EPA's review
here is focused on whether the submitted plan meets the statutory
requirements for attainment of the one-hour ozone standard, and doesn't
interfere with attainment of the 8-hour NAAQS. In reviewing the 1-hour
attainment SIP, EPA did consider consistent with section 110(l) whether
this SIP revision would interfere with attainment of the 8-hour NAAQS.
Section 110(l) requires that any plan revision not interfere with any
applicable requirement concerning attainment and reasonable further
progress, or any other applicable requirement of the Act 42 U.S. C.
Sec.  7410(l). As provided in Section II.E, EPA concludes that these
revisions will not interfere with attainment or progress toward
attainment of the 8-hour ozone NAAQS.
    Comment GC4: The commenter (Wilson) indicated the EPA should reject
the TCEQ claim that the SIP revision is likely to lead to attainment
because it is based on a model analysis that is systematically biased
towards under predicting unhealthy levels of ozone, both in the base
case and future conditions. The commenter continues that TCEQ wrongly
claims the only significant reason for this under prediction is the
under reporting of short-term emissions by industry and that other
factors exist for the under prediction bias. The commenter continues
that because the TCEQ did not recognize the other factors that lead to
the under prediction bias in their model, that the plan being
considered by EPA lacks remedies for each of these factors. The
commenter gives the example that TCEQ did not adopt measures to
regulate VOCs other than HRVOCs and that TCEQ even repealed some
general VOC control measures even though evidence suggests that Other
VOCs (OVOCs) are a factor in the under prediction bias. The commenter
summarizes that since such additional control measures are lacking,
that EPA should disapprove the revisions.
    Response GC4: While EPA agrees that a general under prediction bias
exists in the base case and future year modeling, we disagree that this
is grounds for disapproving the revisions. EPA believes all model
performance measures should be considered and there is no rigid
criterion for model acceptance or rejection in assessing model
simulation results for the performance evaluation. As recommended by
EPA, the State's model performance evaluations for the selected episode
included diagnostic and sensitivity analyses, and graphical and
statistical performance measures. The model performance evaluation
included statistical measures consisting of comparing the modeled
versus monitored ozone that were mostly within the suggested limits in
EPA's guidance. In addition, the graphical performance of the model for
the episode indicated the model performed fairly well. For all days
modeled, the combination of statistical and graphical performance was
deemed sufficient for this revision package.
    Sufficient evidence exists that the episodic emissions that occur
in the Houston area do impact the model's capacity to replicate ozone
and are a plausible reason for much, if not all of the ozone under
prediction in the model. While some evidence exists that an under
estimation of emissions of Other VOCs (OVOCs = VOCs other than HRVOCs)
may exist and that this may be responsible for some modeling under
prediction, the research to answer the level of under/over estimation
of OVOCs and how to allocate such adjustment in the model were not
available when TCEQ was conducting the modeling for these revisions.
Furthermore, modeling analyses indicate that HRVOC emission releases
(in addition to the normal inventory) could result in higher ozone
levels that would be as high as monitored values

and would seem to resolve much of the modeling under prediction bias
issues. While an under estimation of OVOCs may also be part of the
reason for the under prediction bias in the model, sufficient analyses/
evidence do not exist to specifically quantify any level of bias due to
wrongful estimation of OVOCs. While TCEQ did not implement additional
controls on OVOCs, it is EPA's technical opinion that based on the
weight-of-evidence and the modeling, the State's revised control
strategy provides for attainment by November 15, 2007.
    Comment GC5: The commenter (Wilson) indicated that the plan is not
likely to lead to attainment because several of the control strategies
are not likely to be as effective as TCEQ claims. The commenter
continues that EPA should not approve some of the control strategy
revisions (relaxation of NOX controls) in order to maintain
a higher level of pollution control in the Houston area. In other parts
of the commenter's package, the commenter indicated that the
NOX rule revisions should not be approved.
    Response GC5: It is EPA's technical opinion that based on the
modeling results and the additional weight-of-evidence, the State's
revised control strategy provides for attainment of the 1-hour ozone
NAAQS by November 15, 2007. We have addressed other specific comments
from the commenter on issues related to why the control strategies may
not be as effective as TCEQ claims elsewhere in the response to
comments. The Clean Air Act gives the State the primary authority to
prepare a SIP that provides for implementation, maintenance and
enforcement of the NAAQS in each air quality control region and to
determine the mix of control measures to achieve that goal, as long as
they show attainment and the demonstration meets 110(l) requirements.
EPA's responsibility is to review SIPs that the State provides and
either approve or disapprove the revisions based on their meeting the
requirements of the Act. EPA has reviewed the revised SIP and has
determined that the revisions (including the NOX rule
revisions) demonstrate attainment by November 15, 2007.
    Comment GC6: The commenter (Wilson) indicates that although the
TCEQ has exercised sound scientific judgment in responding to many
issues that have arisen, the SIP revision is also characterized by a
pattern of avoiding unwanted findings by withholding data, applying
standards selectively, reaching inconsistent conclusions, failing to
conduct critical research, and unreasonably dismissing comments. The
commenter continues that these actions undermine the technical
credibility of the SIP revision and prejudice its findings. The
commenter indicates that EPA should conduct its own analysis of
available data and apply a health-protective bias whenever more than
one argument is supported by the available data.
    Response GC6: EPA is satisfied with the technical credibility of
TCEQ's finding. As discussed in the response to comment GC5, TCEQ is
responsible for developing an acceptable implementation plan. TCEQ
continues to have an open stakeholder process (both periodic technical
and planning meetings and special meetings). EPA encourages TCEQ to
continue having an open stakeholder process and to continue to share as
much information (analyses, modeling, proposed regulations, etc.) as
possible with the public/stakeholders and allow for comments/feedback
to be considered in the SIP development process. EPA conducted a
detailed review of the proposed revisions prior to proposing approval
and provided detailed review of the modeling and weight-of-evidence
analysis in the proposal and TSD. EPA has also considered the comments
received during the proposal's comment period and has determined that
the SIP revisions are acceptable and EPA is approving these revisions
to TCEQ's SIP.
    Comment GC7: A commenter (Wilson) indicated that TCEQ has failed to
include contingency measures in the HGB ozone SIP. The commenter
continues that TCEQ has claimed they satisfy this requirement with the
measures to be implemented in 2008, since the measures are above and
beyond those modeled in the proposed revision and include additional
TERP reductions. The commenter contends that these measures are not
sufficient because TCEQ has not substantiated how they are sufficient
to advance attainment.
    Response GC7: TCEQ included contingency measures in the SIP
revision for 23.57 tpd reduction in NOX and 10.84 tpd of VOC
in 2008. EPA has reviewed the proposed contingency measures and
concluded that they meet the level of reductions necessary.
Historically, EPA has recommended that contingency measures achieve an
additional 3 percent reduction in emissions. (57 FR 13511) The purpose
of contingency measures is to ensure continued progress while the area
moves forward to adopt additional controls needed for attainment and we
believe an additional 3 percent achieves that purpose. (57 FR 13511) We
are uncertain what the commenter is referring to when it suggests that
contingency measures must be ``sufficient to advance attainment'' but
note that term is not used in the statute nor has EPA ever suggested
that as the test for determining the adequacy of contingency measures.
While we find that TCEQ has adequately satisfied the contingency
measure requirement, ultimately we note that contingency measures for
failing to attain the 1-hour standard will not apply. As noted in the
Phase 1 Rule to Implement the 8-hour ozone NAAQS, EPA did not retain 1-
hour contingency measures as an applicable requirement that would
continue to apply after the 1-hour standard is revoked (i.e., June 15,
2005 for the HGB nonattainment area). EPA also further noted that once
the 1-hour standard was revoked, EPA would no longer make
determinations whether an area had met or failed to meet that revoked
standard and thus contingency measures would not be triggered even if
adopted. (70 FR 30592, May 26, 2005 at page 30599.)
    Comment GC8: A commenter (Wilson) indicated EPA should not
disregard the 1-hour ozone standard in light of the new 8-hour
standard. The commenter indicated that an analysis of the historical
record demonstrates that if Houston meets the 1-hour standard, the
public will be protected from air pollution exposures that would be
allowed under the 8-hour standard. The commenter iterated that it is
likely to be true that for much of the rest of the country the 8-hour
standard can reasonably supplant the 1-hour standard and in Houston the
8-hour standard is clearly superior to the 1-hour standard in terms of
public health benefits. The commenter continued that the 1-hour
standard has a special role in Houston for the protection of public
health. The commenter indicated that TCEQ data suggest that failing to
attain the 1-hour standard will leave Houston residents with exposure
to ozone at levels that the EPA once sought to prevent. According to
the commenter's analysis of days when either the 1-hour and/or the 8-
hour standard were exceeded during 2000-2003, the one-hour standard was
the only standard breached on about 7 percent of the days
(approximately 6 days/year). The commenter also indicated the AQI
reaches a higher value based on the one-hour standard on a similar
number of days. The commenter continued by indicating a singular focus
on the 8-hour standard (and not addressing the 1-hour standard) could
leave Houston residents

breathing unhealthy air about 6 days per year even after the 8-hour
standard is attained.
    The commenter continued that controlling short-term exposures to
ozone is important as many scientific studies based on the 1-hour ozone
standard report increased use of asthma medication, increased emergency
room visits and hospitalization for respiratory problems, even at
levels below 0.12 ppm for just one or two hours with affects continuing
for days or months afterwards.
    The commenter continues that EPA has always viewed the 1-hour and
8-hour standards as adequate alternative methods for protecting public
health, and gave consideration to establishing a standard that combined
both 1-hour and 8-hour measurements. The commenter indicates the basis
for revoking the 1-hour ozone standard dates back to a 1996 report
(EPA, Review of National Ambient Air Quality Standards for Ozone:
Assessment of Scientific and Technical Information, June 1996) issued
by EPA staff that concluded from a public health perspective, a 1-hour,
an 8-hour or a combined standard could be set at a level that would
adequately protect public health. The commenter continues that the
report did not explicitly reject a combination of the 1-hour and 8-hour
standards, but did firmly endorse an 8-hour standard. The commenter
indicates the record isn't entirely clear as to why a combined standard
was not the initial recommendation of staff in the report, but it seems
to turn on the word ``efficient.''
    The commenter continues that EPA concluded later that year in a
report (US EPA, ``Responses to Significant Comments on the 1996
Proposed Rule on the National Ambient Air Quality Standards for
Ozone''; December 13, 1996), based on modeling of ozone exposures,
``that an 8-hour 0.08 ppm averaging time does effectively limit both 1-
and 8-hour exposures of concern. The commenter continues that
subsequent EPA decisions recognize that the 8-hour standard might not
effectively protect the public from 1-hour health effects, and sought
to retain the 1-hour ozone standard until attainment, and then revoke
it on an area-by-area basis. The commenter indicates that this would
have been consistent with full protection of public health and
administrative efficiency.
    The commenter continued that the EPA decided for legal reasons to
go ahead and revoke the 1-hour standard nationwide while California's
current review of its state ozone standards is likely to lead to a 1-
hour standard of 0.09 ppm, compared to the current 0.12 ppm standard
used by EPA.
    The commenter concluded if the plan EPA proposes to approve fails,
Houston could still have serious public health effects due to ozone
smog even if the TCEQ leads Houston to attainment of the 8-hour
standard.
    Response GC8: As we noted in the final Phase 1 Rule, we determined
in the 1997 NAAQS rulemaking (69 FR 23951) that we did not need to
retain the 1-hour standard to protect public health. Thus, in the 1997
NAAQS rulemaking, EPA concluded that the 8-hour standard would replace
the 1-hour standard. The issue of whether the 1-hour standard is needed
to protect public health has not been reopened here and, indeed, should
be considered only in the context of a national rulemaking reviewing
the NAAQS.
2. Comments on the Photochemical Modeling
    Comment M1: Commenter (Wilson) comments that EPA modeling guidance
(1996) indicates that weight of evidence analysis included to
supplement the deterministic and statistical modeling attainment
demonstrations needs to be compelling to overcome the results from the
photochemical grid model. The commenter continues to cite EPA guidance
indicating that ``If the results of corroborative analyses are also
consistent with the conclusion that a strategy will be insufficient to
meet the NAAQS by the statutory date, attainment would not be
demonstrated.'' The commenter continues that the SIP revision does not
meet EPA guidance for demonstrating attainment because: (1) The plan
fails the deterministic test as indicated by the use of weight of
evidence (WOE) to justify dropping the August 31 from the modeling
episode. (2) The databases, in particular emission inventories, used in
the modeling have a number of problems including the failure of TCEQ to
reconcile their own findings about the under-reporting of other VOCs.
The analysis and WOE exhibit a selective approach to the examination of
relevant data that distorts the WOE guidance and results in relaxation
of WOE requirements. (3) The episode days used to evaluate the control
strategy do not include days with observations near, but slightly
above, the design value and meteorological ozone forming potential
likely to be exceeded about once per year as advised by EPA guidance.
(4) The TCEQ's corroborative analyses are also consistent with the
conclusion that the strategy is insufficient to demonstrate attainment.
    The commenter summarizes that a thorough and skeptical
consideration of TCEQ's technical analysis must result in the EPA
finding that the SIP revision does not demonstrate attainment of the 1-
hour ozone standard. The commenter continues to indicate: (1) The
modeling has a systematic ozone underprediction bias at levels above
120 ppb. (2) TCEQ's attainment demonstration has failed to address this
shortcoming in the WOE and the plan does not include control measures
to adequately control emissions on ``level purple'' ozone days that are
representative of the region's design value. (3) The control measures
included in the plan are inadequate to meet even the expectations of
the TCEQ. The commenter then indicates that EPA should not approve the
SIP revision, and instead find that TCEQ has failed to submit a plan
providing for implementation, maintenance, and enforcement of the ozone
NAAQS for the HGB area.
    Response M1: As also discussed in other responses, EPA did not
dismiss any measures or analyses used by TCEQ for their model
performance evaluation, nor did EPA disagree with TCEQ's conclusion,
based on the modeling and in conjunction with the WOE analyses, that
this SIP revision should result in the HGB area attaining the 1-hour
ozone standard by November 15, 2007. EPA's analysis included evaluating
model performance and model reaction on the August 31st episode day in
conjunction with the additional WOE materials that TCEQ provided for
this day, as well as the rest of the attainment demonstration period.
The commenter raised a number of specific issues that are addressed in
this comment or more specifically addressed in separate comments, but
the combination of the comments do not sway EPA's technical opinion
that the modeling and the combined Design Value (DV) approach predicts
the area will reach attainment by the end of 2007.
    EPA also reviewed modeling sensitivities conducted by TCEQ
including rough adjustments to OVOCs, but concurred with TCEQ that the
body of supporting material to conduct a refined adjustment for OVOCs
did not currently exist. EPA encourages TCEQ to continue to research
this issue to address this uncertainty in the future and further
address this issue in the 8-hour ozone SIP. EPA believes that most of
the error can be best explained by uncertainties in the amount of HRVOC
that were actually emitted and the spatial allocation of the HRVOC
adjustment and meteorological model issues. TCEQ chose an average value
for the adjustment factor for the HRVOCs

and adjusted the same level over the entire Houston/Galveston/Brazoria
area, even though field study data indicates that a range existed that
was many times higher than the value utilized in TCEQ's modeling in
some cases. The TCEQ and EPA agree that there is simply not enough data
available at this time to precisely locate all of the sources of non-
inventoried HRVOC emissions. The TCEQ is pursuing several areas of
research that will use additional monitoring data and other data to
improve the spatial and temporal allocation of HRVOC emissions, and is
simultaneously pursuing bottom-up methods to improve emissions
inventories. These efforts will allow a much more refined treatment of
``extra'' hydrocarbon emissions in future modeling. TCEQ should
continue to strive to yield better estimates in HRVOC and OVOC
emissions from industrial facilities in HGB and this should continue to
be one of the focus areas for the second TEXAQS study in 2005-2006. EPA
agrees that TCEQ made an appropriate estimate of how the emission
inventory for HRVOCs should be adjusted without sufficient data to
conduct a higher level of adjustment with spatial variability. TCEQ
tried to gather more data through a special inventory request of over
80 industrial facilities in the HGB area, but was not able to collect
all of the data required to conduct a more accurate HRVOC adjustment.
We believe our understanding of the process is sufficient, however, to
interpret the photochemical model results and determine that this SIP
revision is approvable.
    EPA previously reviewed and agreed that the episode (8/21-9/6/2000)
was appropriate for this SIP revision. The episode did include several
days (8/25, 8/30, 8/31, and 9/5) that included surface level monitored
data greater than 175 ppb and several days near the area's design value
at the time of the episode and the episode did have the benefit of
intensive data collected during this period. Given the historical
difficulty with obtaining acceptable photochemical model performance in
the HGB area, EPA recognizes the importance of selecting days from a
field study period in preference to other non-field study days. On
these high ozone level days (>175 ppb) the commenter is correct that
the model had an under prediction bias of the domain peak and at many
monitors (values above 120 ppb). But this is thought to be largely the
result of many issues (HRVOC adjustments and the two-pronged design
value approach, meteorological issues, general modeling issues, etc.)
discussed above and in other responses, but was determined acceptable
in this SIP revision due to the inclusion of HRVOC rules that will
remove much of the variability in HRVOC emissions and result in
significantly lower HRVOC emission levels. It should also be noted that
on these four high ozone level days ( >175 ppb monitored), EPA's three
primary ozone statistic metrics were within EPA guidance parameter for
all four days (including the August 31st) with the exception of the
Peak Prediction accuracy metric on the August 30th (see TSD Tables G.1-
1 to G.1-3 and Texas SIP materials for details).
    The need for further studies does not mean, however, that the
modeling relied upon today was unable to estimate the amount and type
of emission reductions needed for attainment. EPA believes because the
diagnostic/sensitivity tests do not reveal serious flaws in model
formulations and the model generally predicts the right magnitude of
the peak which is confirmed by the statistical measures and graphical
analysis, that the model does provide an acceptable tool for estimating
the amount of emissions reductions needed. It is EPA's technical
opinion that based on the modeling and the weight-of-evidence, the
State's control strategy should provide for attainment by November 15,
2007.
    TCEQ and others have provided significant amounts of modeling
sensitivities, monitoring analyses, etc. as part of the corroborative
analyses that were evaluated in the decision to propose approval of the
SIP revisions. While some components of the corroborative analysis seem
to indicate that the SIP revision plan may not succeed, a majority of
the components indicate that the plan will succeed. EPA has weighed
many different analyses from TCEQ and others (including the HARC H12
and H13 project results) and concluded that the SIP revision plan will
attain by the attainment date. TCEQ has agreed to conduct further
refinements to the emission inventory and meteorology of this episode
in development of the 8-hour ozone SIP. TCEQ and others are also
conducting another field study in 2005 and 2006. TCEQ has indicated
that they will attempt to weigh any new information derived from the
further studies and evaluations, and incorporate the information into
the HGB 8-hour Ozone SIP to be submitted to EPA by June 15, 2007.
    Comment M2: The commenter (Wilson) commented that they are
concerned with final episode selection and with the modeling results
for that episode. The commenter continued by conjecturing that the
episode included in the modeling does not contain enough days with
observations near, but slightly above, the design value and with
meteorological ozone forming potential that is likely to be exceeded
about once per year as is advised by EPA guidance. The commenter also
indicated that the SIP revision adequately addresses Air Quality Index
(AQI) level ``Orange'' ozone days and not ``Purple'' level ozone days
when the HGB area has a AQI level ``Purple'' ozone problem.
    The commenter continued, the 2003 design value for the 1-hour ozone
standard was 0.175 ppm and for the period 2000-2003, air pollution
monitors recorded an average of 9 days per year with a 1-hour ozone
measurement over 0.165 ppm, and about 1 additional day per year
measured over 0.205 ppm. The commenter summarized this data as on
average during the HGB area has 10 AQI level ``Red'' and ``Purple''
days per year during the 2000-2003 period.
    The commenter also indicated that according to ground-level
monitoring data used by the TCEQ in its plan, the episode used for
control strategy evaluation in the proposed SIP does not provide ozone
formation conditions that are close to the region's design value, and
that it does not resemble the character of the region's serious ozone
problems. The commenter provided a graph to illustrate that the plan's
best effect is shown by reducing several AQI level ``Orange'' days near
the 1-hour ozone standard of 0.12 ppm, but no AQI level ``Red'' or
level ``Purple'' days. The commenter also indicated that aircraft data
and Williams tower data did include higher AQI levels of ``Red'' and
``Purple'' in some of the areas that do not have ground monitoring
stations with the caveat that some of this data was of shorter duration
period.
    The commenter continued that: ``The TCEQ estimates the effect of
the undocumented emission releases by calculating an alternative design
value of 144 ppb for comparison to the actual design value of 182 ppb
for the 1999-2001 period.'' The commenter further indicated that
another perspective is suggested by comparing the model variability in
peak ozone to actual variability and concludes that routine variability
on days conducive to ozone formation is limited to only about 20 ppb,
compared to about 75 ppb of actual variability in ozone formation
observed at ground monitors. The commenter concludes that regardless of
whether one concludes that 38 ppb (182 ppb-144

ppb) or 55 ppb (75 ppb-20 ppb) of peak ozone formation are not properly
modeled, the challenge to the weight-of-evidence analysis is clearly
substantial.
    Response M2: The original episode selection of August 19-September
6, 2000 was selected by TCEQ with EPA review and comment on the
selection of the episode. This TexAQS 2000 episode was selected because
it includes a 19-day window with both weekday and weekend events, a
suite of wind directions, and daily ozone peaks measured in several
different areas of the city reflecting the net surface transport during
each day. When combined with the additional meteorological and
precursor data collected during the TexAQS 2000 study period, this
extended ozone episode includes a better than normal monitored data set
and a fairly representative mix of HGB area episode types. Given the
historical difficulty with obtaining acceptable photochemical model
performance in the HGB area, EPA recognized (as allowed by EPA modeling
guidance) the importance of selecting days from a field study period in
preference to other non-field study days during the episode selection
process with TCEQ. EPA's modeling guidance for the 1-hour ozone NAAQS
(``GUIDELINE FOR REGULATORY APPLICATION OF THE URBAN AIRSHED MODEL'';
U.S. EPA; July 1991; pg. 11) includes the following text:

In choosing from among the top-ranked episode days, consider the
availability and quality of air quality and meteorological data
bases, the availability of supporting regional modeling analyses,
the number of monitors recording daily maximum ozone concentrations
greater than 0.12 ppm (i.e., pervasiveness), number of hours for
which ozone in excess of 0.12 ppm is observed, frequency with which
the observed meteorological conditions correspond with observed
exceedances, and model performance (discussed in Chapter 5). For
example, the top-ranked episode day within a meteorological regime
may have only routine air quality and meteorological data bases
available for use in the modeling. The third-highest day, however,
may have occurred during an intensive field study, so that a more
comprehensive data base is available. Thus, the third-highest day
may be more desirable for modeling than the top-ranked day.

    As EPA's guidance indicates, days with not quite as high ozone
exceedances may be chosen over the highest ozone day if they occurred
during an intensive field study. Given the difficulties and
uncertainties with modeling the Houston area, EPA approved the
selection of the field study period as the episode period to be modeled
in accordance with EPA's guidance. It should be noted that the 1-hour
ozone design value is calculated for each monitor in the domain and is
the 4th highest 1-hour ozone value in a three year period (see EPA's
memo titled ``Ozone and Carbon Monoxide Design Value Calculations'';
June 18, 1990). Therefore the design value for the area is usually
lower than the 1st high value as the commenter indicated, and for the
limited time period (2000-2003) that the commenter analyzed, the HGB
area design value was not a ``Purple'' level AQI day, but a mid ``Red''
level AQI day.
    Based on model performance issues, the original episode was reduced
to August 25, 26, August 29-September 4, and September 6, 2000. As TCEQ
identified in their response to comments, it is important to note that
six 1-hour ozone exceedance days were included in the ten day modeling
period (August 25-September 1), and the average of those peaks was
168.3 ppb. This modeled period of the episode did include several days
(8/25, 8/30, 8/31, and 9/5) that included surface level monitored data
greater than 175 ppb and several days near the area's design value at
the time of the episode and the episode did have the benefit of
intensive data collection that occurred during this period. The
September 5th day was dropped due to model performance issues. On these
high ozone level days (>175 ppb) the commenter is correct that the
model had an under prediction bias of the domain peak and at many
monitors (values above 120 ppb), but this is thought to be largely the
result of many issues (HRVOC adjustments and the two-pronged
alternative design value approach, meteorological issues, general
modeling issues, etc.). As discussed in other responses, the modeling
was determined to have an acceptable model performance. Even with an
under-prediction bias, six of the Base 5b episode days had values
greater than 150 ppb in the basecase modeling which is higher than the
Alternate Design Value (ADV) of 144 ppb that TCEQ used (and 7 days
above 144 ppb, see TSD Table H-3). In evaluating the TSD tables, the
modeling episode included three monitored ``Red'' AQI level days, with
two of the days near ``Purple'' levels (8/25 and 8/30). With the
combined strategy of reducing emission events and routine emissions,
EPA would not expect the basecase modeling (utilizing a routine
emission approach) to include ozone levels above the design value.
Furthermore, TCEQ did include many days that were above the 144 ppb ADV
that they used and thus we weighted this fact as a conservative WOE
element. We also concurred with the selection of this episode and that
it included enough high ozone value days with values near the design
value to be the basis for attainment demonstration modeling.
    Comment M3: Commenter (Wilson) comments that the episode used for
control strategy evaluation in the proposed SIP does not provide ozone
formation conditions that are close to the region's design value, and
do not resemble the character of the region's ozone problems with the
under prediction of the peaks and the modeled peak 1-hour ozone levels
only varying approximately 20 ppb for each day between the base and
future attainment demonstration modeling. The commenter then continues
that TCEQ's response is the under prediction of the peaks is likely due
to unreported or under-reported releases of HRVOCs and that EPA
concurred in this assessment of the model performance with citations
from EPA's Technical Support Document. The commenter continues that
TCEQ estimated the effects of undocumented releases by estimating an
Alternative Design Value (ADV) of 144 ppb compared to the actual design
value of 182 ppb for the 1999-2001 period. The commenter then discusses
an alternate approach to an ADV based on the routine variability of
only 20 ppb in the modeling. The commenter summarizes that the two
approaches yield either a 38 ppb or a 55 ppb level of peak ozone that
is not modeled properly and that the challenge to the WOE is
substantial.
    The commenter continued that EPA properly expressed some skepticism
that under-reported, short-term emission releases should explain the
entire under-prediction of peak ozone levels, with a cite from EPA's
TSD. The commenter concludes that EPA should further conclude that
several other factors are equally likely causes of the under-prediction
of ozone peaks by model analysis: Failure to use superfine grid, under-
reporting of OVOCs (both routine and short-term), and underestimation
of emissions from ports and heavy duty diesel trucks. The commenter
also indicated that the drop in ozone design values over the last
several years is due to the implementation of NOX RACT and
favorable meteorology.
    Another commenter (BCCAAG) commented in favor of the ADV approach
and the ADV value of 144 ppb as utilized by TCEQ. The commenter
continued that the strength of TCEQ's WOE demonstration is bourne out
by the recent decreases in ozone values

(Design values,  of days of exceedances,  of 1st and
2nd High values) in HGB. The commenter continues that this occurred
despite an increase in ozone monitors and economic growth in the
region.
    Response M3: As previously discussed in the response on M2, EPA
concurred that this was a reasonable episode for this SIP revision and
that it included enough days with high ozone levels. The commenter is
correct in indicating that for most days the modeled change between
base and 2007 future controlled level is less than the difference
between the daily monitored peak and 124 ppb, but the daily difference
value ranges from 14.7-37.6 ppb with an average of approximately 27.5
ppb (not 20 ppb). EPA conducted further analysis of TSD tables G.1-2
and G.1-3 in preparing response to this comment. The original episode
had 19 days with 13 exceedance days with an average of 1-HR daily
maximum ozone of 160 ppb (36 ppb above attainment) and a range of
exceedances from 125 to 200 ppb for the exceedance days. This SIP
included a shorter period due to model performance issues that included
nine exceedances with an average of 159 ppb and a range from 125 to 200
ppb (based on surface measurements).
    The commenter lists a number of issues--failure to use superfine
grid, under-reporting of OVOCs (both routine and short-term); and
underestimation of emissions from ports and heavy duty diesel trucks--
that may be part of the reason for the under-prediction bias and did
consider these issues in the TSD that was the basis for our proposal.
We discuss these specific issues in other responses in this notice, but
we believe that these issues, in conjunction with other issues
(including under/unreported emissions) that we have discussed in other
responses, covers most of the issues that may be causing the under-
prediction bias. Specifically, we have concluded that one of the
greatest components of uncertainty in the modeling system is the
variability and under/unreported emissions issue. The measures included
in this revision will help to resolve the level of uncertainty in this
area. As noted elsewhere in this document, we have reviewed the model
performance, including bias issues, and have determined the modeling
demonstration to be acceptable.
    Comment M4: Commenter (Wilson) comments that the TCEQ should have
developed a robust method of relating one- and five-second interval
ozone data collected by moving aircraft to one hour ozone estimates
measured by stationary ground monitors so that airborne monitoring data
may be used to estimate 1-hour ozone values in areas of the HGB area
that are far from ground monitoring stations.
    Response M4: EPA agrees that such a methodology would be a useful
analytical tool and TCEQ did initiate a study with the Pacific
Northwest National Laboratory to discuss and illustrate problems
associated with comparing observations from an airborne monitoring
platform to results from photochemical model grids (which might be used
with ground based monitoring data). Developing such a methodology is a
complex issue since the methodology must take into account temporal
differences in the data (i.e. one second interval for airborne data
versus a five minute interval for ground data), spatial differences in
the monitors (differences in location and elevation), and environmental
differences for the monitoring equipment (temperature, humidity, solar
radiation, etc.) and potentially varying levels of sensitivity/accuracy
between the different instruments utilized.
    Monitors measure concentration at a point in space and in reality,
these concentrations can vary significantly over a grid cell or an
area. This is true especially for ozone if it is contained in a narrow
plume. Inevitably, a grid type model will smooth some natural phenomena
because natural conditions are averaged over the volume of each grid
cell. For instance, model output represents a volume average, typically
4 km x 4 km by 50 meter column. As a result, reasonable comparisons
between model predictions and monitor observations are not expected to
match exactly. With reasonable performance, time series typically show
similar diurnal cycles but not exact concentration levels. As a result,
it is very difficult to obtain a precise equality between modeled
concentration and monitored concentration. This is to be expected and
does not necessarily call into question the model's utility as a tool
to predict the level of emission reductions needed to reach attainment.
As stated in previous comments, EPA believes the model provides
reasonable predictions of ozone levels as confirmed by comparisons with
monitoring data and therefore can provide an acceptable estimate of the
amount of emissions reductions needed for attainment.
    Comment M5: Commenter (Wilson) commented that aircraft data were
excluded from the model performance evaluation. The commenter also
commented that the TCEQ should have revised the base case model
performance evaluation section to include qualitative evaluation of
model performance based on aircraft data, including reconsideration of
alternative model approaches that may appear more favorable in light of
these data.
    The commenter then indicated that TCEQ had performed a comparison
of model results to aircraft data, but inadvertently omitted this
comparison from Appendix B of TCEQ's proposal. Due to this omission
during TCEQ's proposal, the commenter indicates that they have reviewed
the TCEQ's analysis and are providing comments on TCEQ's Appendix B
analysis.
    The commenter then indicates that they calculated a value of 89
percent as the difference between 1-hour and 5-minute peaks at the Deer
Park Monitor on October 7, 1999 (30 ppb difference). The commenter's
analysis then utilized this 89 percent factor to scale aircraft data to
1-hour ozone values for comparisons on August 25-30, and September 1,
3, 4, and 6th.
    The commenter then continued to give specific analyses of aircraft
observations to model predictions for each of these days. The commenter
utilized the 89 percent factor to indicate that August 25, 30, and
September 1st were days that aircraft and surface monitoring data
showed levels well above those achieved in the model. The commenter
also utilized the 89 percent factor to indicate that aircraft data
showed ozone levels above both the surface monitoring data (maximum of
146 ppb) and model performance data (maximum of 151 ppb) for August
29th.
    The commenter also utilized the 89 percent factor to conjecture
that TCEQ incorrectly assessed that the model over-predicted ozone
formation on August 27 and 28 and that the aircraft data suggests that
the model does accurately predict ozone levels. The commenter then
continued on that the model under-predicts high ozone levels above 120
ppb.
    Response M5: TCEQ did include the Appendix B materials in the SIP
submitted to EPA and EPA reviewed the Appendix B as part of the review
conducted for the proposal notice. Aircraft observations can be useful
in assessing model performance, but must be done with care, due to the
many issues outlined in Response M4. Due to these technical concerns it
is difficult to utilize aircraft data other than in a qualitative/
directional sense for comparing aircraft observational data to 4 km
hourly grid modeling predictions.
    The commenter did not provide the data utilized to calculate the 89
percent conversion value to convert aircraft data into an estimate of
1-hour ozone concentrations. The commenter did indicate that this value
was calculated

using only one day of data at one monitor in the HGB area for a day
that is not during the modeled episode period and for a day (October 7,
1999) that is not even during the main period of ozone season in the
HGB area. No analysis was provided to document that this was a typical
day, or a typical data set to estimate the 89 percent conversion factor
nor was an effort made to make sure the data sample set for this
calculation was appropriate. This 89 percent value seems high from
discussion within EPA Region 6 including monitoring staff that
typically review the 5-minute data and 1-hour data. Furthermore the
commenter has made several assumptions in their analysis that they
utilize to support their comment, that actually weakens their analysis.
The commenter assumed that 5-minute data is the approximate length of
time that is representative of the aircraft data in comparison to a
model grid square, although no basis was given. The method does not
resolve that an aircraft would be a line sample through a model grid
square at an altitude that does not have hourly monitored data and
would not be the same sampling as a single monitor (if you could have
one at the altitude of the aircraft). The commenter did not adjust for
a model that calculates a large volume average versus an aircraft that
is a shorter duration line sample through multiple grid cells that may
be several hundreds of meters thick for the layer of the model that the
aircraft would be flying. Due to all of these issues including the very
limited data set that the 89 percent was generated, we have to discount
any assessments that utilized the 89 percent factor.
    While the commenter is correct that comparing ground observations
to modeled values, the model does under-predict ozone concentrations
above 120 ppb for some of the days. As discussed in response to
comments elsewhere in this notice, this is expected and was fully
reviewed and determined to be approvable for this SIP revision.
    Comment M6: The commenter (Wilson) indicates that the exclusion of
one kilometer resolution modeling is arbitrary and unreasonably biases
the results in favor of an attainment finding. The commenter continues
by disagreeing with EPA's proposed action and requests that EPA
evaluate the one kilometer resolution modeling as useful evidence that
the attainment demonstration is insufficient. The commenter argues that
the TCEQ has failed to present a compelling technical argument for
excluding one kilometer resolution from the base case and control
strategy evaluations. The commenter included language from TCEQ emails,
that were included in the materials that were reviewed by EPA while
developing the proposal and TSD for this action. The commenter asserts
that TCEQ made the decision to exclude one kilometer modeling prior to
attempting to develop an technical justification for the decision. The
commenter indicates that peak ozone levels are often higher for one
kilometer modeling, but other model performance statistics are
relatively unchanged when the one kilometer modeling output is compared
to the four kilometer average of the one kilometer resolution output.
The commenter concluded that the one kilometer resolution modeling made
attainment demonstration more difficult and therefore EPA should
consider that statistics do not degrade and the peak ozone levels are
better represented with the one kilometer modeling, that EPA should not
approve the demonstration because the one kilometer grid modeling
predicts nonattainment on several days for control strategy
evaluations.
    Response M6: While the commenter asserts that EPA should reconsider
our analysis of the appropriateness of the one kilometer resolution
modeling, no new information was provided that was not previously
considered in our review during the development of the proposal and TSD
for this action. We would like to point out that a full model
performance analysis (including statistics, graphical plots, and
emissions sensitivities) were not provided for the one kilometer
resolution modeling by the commenter or in the TCEQ SIP revisions, so
that a full model performance analysis could be compared with four
kilometer model performance analysis. Without such an analysis, it is
difficult to ascertain whether one kilometer resolution modeling is
actually better performing (as the commenter claims) than four
kilometer resolution modeling or just yielding higher peak ozone
values.
    As was discussed in the TSD, concerns have been raised by the
academic community that while the CAMx model will give model
predictions at 1 km, it has never been fully evaluated for correct
performance at this scale in the HGB area and that the uncertainties
associated with these concerns may undermine the credibility of the
model runs upon which the control strategy was based. Some of the
parameters within CAMx which raised concerns include
horizontal and vertical diffusivities and assumptions within
CAMx that apply to the hydrostatic equilibrium of horizontal
and vertical transport may begin to break down at a finer grid
resolution.
    TCEQ indicated in their response to comments that continued
evaluation and peer review of these uncertainties is necessary before
the model can routinely be applied at a finer resolution to replicate
all conditions of ozone formation.
    For further discussion of technical concerns with utilizing the one
kilometer resolution modeling and EPA's thoughts and review of the
issue please see the proposal and TSD for this action.
    Comment M7: The commenter (Wilson) comments that while short-term
HRVOC emission events are surely a frequent and significant cause of
ozone formation in the Houston area, the TCEQ overstates their role.
The commenter continues that TCEQ failed to consider specific problems
with its data, and then TCEQ made broad statements that are not
supported by their analysis. The commenter then indicates that a more
rigorous analysis would support a smaller, yet still significant, role
in the SIP.
    The commenter then commented on a TCEQ analysis of August 30
indicating that it demonstrated an example of how the TCEQ failed to
identify weaknesses in its control strategy by inconsistent analysis.
The commenter stated that TCEQ suggests that the gap between the
modeled peak of 0.137 ppm and the observed peak of 0.200 ppm on August
30 could be explained by the evidence that one or more emission events
not accurately represented in the modeling inventory occurred on this
day. The commenter continued, that on the other hand, the TCEQ
conducted a sensitivity analysis with a hypothetical upset included on
August 30, but the model peak only increased to 0.145 ppm. The
commenter further indicated that TCEQ minimized the importance of
emission events on ozone formation by finding that ``emission
variability of roughly 1000 lb/hr should be expected in the regions
upwind of peak, region wide ozone concentration at least once per year
and that releases over approximately a two to three hour period can
lead to increases of 2-3 ppb in peak ozone concentration per 1000 lb of
additional HRVOC emissions. The commenter concluded that although two
different TCEQ approaches to modeling short-term emission events
suggest that the hypothesized releases of August 30 could be expected
to cause 4 ppb to 9 ppb of additional ozone, the TCEQ appears to
consider this an acceptable explanation for the 43 ppb gap between the
model and measured peak ozone levels.
    The commenter also indicated that TCEQ failed to properly analyze
the

impact of short-term events on ozone formation because of TCEQ's
failure to question whether the inventory of emissions caused by short-
term releases is accurate in light of the many problems with emissions
inventories. The commenter continues that self-reported upset data are
estimated using methods that have been called into question for many
sources, including flares, cooling towers, storage tanks and fugitive
leaks. The commenter gives the example that flare emissions are
routinely calculated assuming flare performance is at optimal levels,
an assumption that has been questioned by the TCEQ in its technical
analysis (e.g., the ``big smoky'' August 30th flaring event) and by the
EPA.
    The commenter then criticizes TCEQ for TCEQ's remarks on an absence
of evidence available at this time to warrant a correction factor for
under-reported upset emissions and as a result, TCEQ decided to not
conduct a speculative sensitivity analysis. The commenter continued
that on the other hand TCEQ indicated that unreported/underreporting of
short term releases of HRVOCs is responsible for the underprediction
bias in the modeling on some days.
    The commenter concludes that TCEQ's failure to assess the accuracy
of the upset inventory causes EPA to speculate on the implications of
this omission and exactly how much of the underprediction bias is due
to unreported/underreported emission events.
    Response M7: As we discussed in our proposal and TSD, the
attainment strategy is based on a two-pronged approach: control of
routine emissions and a short-term limit to control emission events.
The TCEQ indicated that the influence from short-term releases must be
removed from the area's design value to determine the design value
based on routine emissions. This alternative design value theoretically
will more closely correspond to the routine urban ozone formation
captured by the model. To remove influence of short-term releases, TCEQ
applied Blanchard's technique on the 1999-2001 AIRS data. This
technique uses a threshold of a 40 ppb rise in ozone concentration in
one hour to distinguish sudden rises from the more typical case where
ozone increases more gradually. Removing all days with identified
sudden ozone concentration increases (SOCI), an alternate design value
of 144 ppb was calculated by TCEQ. Final base case (i.e., Base 5b)
includes seven days with modeled peak ozone greater than 144 ppb, so
the modeled peaks in fact, represent very well the TCEQ estimated (non-
SOCI) design value.
    EPA considers the alternative design value approach a reasonable
tool in evaluating the possible impact of non-routine emission
releases, particularly releases of HRVOCs on the design value. By
removing the days that have rapid ozone formation and therefore are
possibly the result of large releases, it is possible to get a sense of
the impact of emission releases on the design value. We are not
convinced that all occasions where ozone rises by 40 ppb from one hour
to the next are caused by releases. Some of these events could be
caused by continuous plumes of ozone sweeping across a monitor as winds
shift direction. These issues take some of the benefit away. In
addition, other studies (including H13) of the frequency of reported
emission events have indicated that the occurrence of reported events
in the right location at the right time in order to impact peak ozone
levels only occurs with a small percentage of non-routine releases.
Still, we agree that emission events do impact the design value to some
degree. Therefore, we agree that considering the alternative non-SOCI
design value provides additional evidence that the future design value
will reach the standard in the future case.
    We disagree with the commenter's criticism of TCEQ's analysis of
August 30th. The 30th had a large flaring event that was likely
underestimated even with the hypothetical run by TCEQ as the
photographs indicate the flare was not completely combusting the
emissions. TCEQ considered a hypothetical situation and was
conservative (both TCEQ and EPA's TSD include this evaluation) in
estimating the true level of emissions present. TCEQ's analysis does
indicate that their hypothetical event would impact the ozone levels
significantly and if actual emissions data were available to model, it
would likely show a much larger impact. TCEQ's analysis was to support
that at a minimum, the ``big smoky'' flare event could have a
significant impact on the 30th and other such events would yield
similar results. Furthermore, the flare sensitivity does not have to
explain all of the underprediction bias on the 30th as many other
factors (meteorology, emissions from other sources, etc.) also can
result in such a bias.
    Furthermore, without the additional monitoring of units in HRVOC
service that is included in this SIP revision, it is impossible to
determine the absolute accuracy of HRVOC emission estimates from flares
and similar emission sources. Therefore neither TCEQ nor EPA, could
completely assess the full extent to which that HRVOC emission events
impact daily ozone levels. TCEQ has required monitoring and restriction
of HRVOC emissions that will reduce the chance of these types of
emissions impacting ozone exceedances levels.
    As we indicated in the TSD for this notice, other studies
(including H13) of the frequency of reported emission events have
indicated that the occurrence of reported events in the right location
at the right time in order to impact peak ozone only occurs with a
small percentage of non-routine releases. The H13 study relied on
reported emission events that are likely underreported and also should
be considered a conservative estimate of potential impacts from short-
term HRVOC emission events since some events are larger than the levels
modeled and ozone formation is not linear. TCEQ determined, and EPA
concurs, that it is necessary to reduce the frequency of emission
events so that emission events do not interfere with attainment of the
1-hour NAAQS, which only allows an average of one exceedance per year.
Based on our review, we believe the hourly emission limit will achieve
this goal. Because facilities would be expected to take action to avoid
emissions events exceeding the short-term limit of 1,200 lbs/hr, we
anticipate that the frequency of such events in the future will be
lower than in the past and therefore less than one event per year
impacting peak ozone should be expected. Even though emission levels
above 1,200 lbs/hr do not count towards the Annual Cap, the Annual Cap
level is low enough that a source could not operate at a 1,200 lb/hr
rate for extended periods without severely impacting its Annual cap
level that is on the order of 2,000 lbs/day or less for most facilities
(maximum cap is 2,419 lbs/day). For more details about the relationship
of the short-term limit and annual cap, please see the response for
comment M8, the proposal and TSD materials.
    The commenter criticizes TCEQ for not estimating the level of under
reporting and unreported emissions, but without flow monitors and other
monitoring requirements on HRVOC emissions (that are being approved as
part of this revision), it would be pure speculation by TCEQ without
any strong basis.
    Comment M8: The commenter (Wilson) comments that TCEQ
inappropriately assumed that upset emissions will not occur in the
future. The commenter continues that TCEQ should have considered the
chance for upset emission events to occur in the

future in its weight-of-evidence analysis.
    Response M8: While the structure of the HECT and the HRVOC rules
anticipates that emission events will not be completely eradicated, EPA
believes that in combination these programs provide sufficient
disincentives that sources will reduce the frequency and magnitude of
large emissions events such that emission events would not be expected
to impact peak ozone levels. The University of Texas report ``Variable
Industrial VOC Emissions and Their Impact on Ozone Formation in the
Houston Galveston Area,'' April 16, 2004, estimated from historic
information that it is probable that at least one event will occur
annually at a time and location to impact peak ozone. It is therefore
necessary to reduce the frequency of emission events so that emission
events do not interfere with attainment of the 1-hour NAAQS, which only
allows an average of one exceedance per year. Based on this study, we
believe the hourly emission limit will achieve this goal. Because
facilities would be expected to take action to avoid non-routine
emissions events exceeding the short-term limit of 1,200 lbs/hr, we
anticipate that the frequency of such events in the future will be
lower than in the past and therefore less than one event per year
impacting peak ozone should be expected.
    Based on the final HECT allocation scheme updated March 20, 2006,
the largest allocation is 441.9 tons. This allocation is approximately
equivalent to 100.9 lb/hr, assuming the facility will operate with the
allocation as an hourly average to represent routine emissions.
Therefore, the largest HECT allocation will be approximately twelve
times smaller than the 1200 lb/hr short-term limit. For every other
source under the HECT, the disparity would be even greater. Based on
this difference between the short-term limit and presumed routine
emissions levels, no source would be able to operate at the hourly
limit for an extended period of time without pushing its emissions
total close to or above the annual cap. Therefore, as discussed in our
proposal, only truly non-routine emissions are expected to exceed the
hourly limit. Furthermore, all exceedances of the 1200 lb/hr limit are
subject to enforcement, which should act as a further deterrent to
excess emissions events.