Approval and Promulgation of Air Quality Implementation Plans; Texas; Revisions to the Ozone Attainment Plan for the Houston/Galveston/Brazoria Nonattainment Area, 58119-58138 [05-19994]

Agencies

• ENVIRONMENTAL PROTECTION AGENCY

[Federal Register Volume 70, Number 192 (Wednesday, October 5, 2005)]
[Proposed Rules]
[Pages 58119-58138]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 05-19994]



[[Page 58119]]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[R06-OAR-2005-TX-0018; FRL-7980-6]


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: Proposed rule.

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SUMMARY: EPA is proposing to approve revisions to the State 
Implementation Plan (SIP) for the State of Texas as it applies to the 
Houston/Galveston/Brazoria (HGB) Ozone nonattainment area. These plan 
revisions result from more recent information on ozone formation in the 
Houston/Galveston area indicating that a combination of controls on 
oxides of Nitrogen (NOX) and highly reactive volatile 
organic compounds (HRVOCs) should be more effective in reducing ozone 
than the measures in the previously approved plan which relied almost 
exclusively on control of NOX. Approval of these revisions 
will incorporate these changes into the federally approved SIP.

DATES: Comments must be received on or before November 4, 2005.

ADDRESSES: Submit your comments, identified by Regional Material in 
EDocket (RME) ID No. R06-OAR-2005-TX-0018, by one of the following 
methods:
     Federal eRulemaking Portal: https://www.regulations.gov. 
Follow the on-line instructions for submitting comments.
     Agency Web site: https://docket.epa.gov/rmepub/ Regional 
Material in EDocket (RME), EPA's electronic public docket and comment 
system, is EPA's preferred method for receiving comments. Once in the 
system, select ``quick search,'' then key in the appropriate RME Docket 
identification number. Follow the on-line instructions for submitting 
comments.
     U.S. EPA Region 6 ``Contact Us'' Web site: https://epa.gov/
region6/r6coment.htm Please click on ``6PD'' (Multimedia) and select 
``Air'' before submitting comments.
     E-mail: Mr. Thomas Diggs at diggs.thomas@epa.gov. Please 
also cc the person listed in the FOR FURTHER INFORMATION CONTACT 
section below.
     Fax: Mr. Thomas Diggs, Chief, Air Planning Section (6PD-
L), at fax number 214-665-7263.
     Mail: Mr. Thomas Diggs, Chief, Air Planning Section (6PD-
L), Environmental Protection Agency, 1445 Ross Avenue, Suite 1200, 
Dallas, Texas 75202-2733.
     Hand or Courier Delivery: Mr. Thomas Diggs, Chief, Air 
Planning Section (6PD-L), Environmental Protection Agency, 1445 Ross 
Avenue, Suite 1200, Dallas, Texas 75202-2733. Such deliveries are 
accepted only between the hours of 8 am and 4 pm weekdays except for 
legal holidays. Special arrangements should be made for deliveries of 
boxed information.
    Instructions: Direct your comments to Regional Material in EDocket 
(RME) ID No. R06-OAR-2005-ST-0018. EPA's policy is that all comments 
received will be included in the public file without change, and may be 
made available online at https://docket.epa.gov/rmepub/, including any 
personal information provided, unless the comment includes information 
claimed to be Confidential Business Information (CBI) or other 
information the disclosure of which is restricted by statute. Do not 
submit information through Regional Material in EDocket (RME), 
regulations.gov, or e-mail if you believe that it is CBI or otherwise 
protected from disclosure. The EPA RME website and the Federal 
regulations.gov are ``anonymous access'' systems, which means EPA will 
not know your identity or contact information unless you provide it in 
the body of your comment. If you send an e-mail comment directly to EPA 
without going through RME or regulations.gov, your e-mail address will 
be automatically captured and included as part of the comment that is 
placed in the public file and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses.
    Docket: All documents in the electronic docket are listed in the 
Regional Material in EDocket (RME) index at https://docket.epa.gov/
rmepub/. Although listed in the index, some information is not publicly 
available, i.e., CBI or other information whose disclosure is 
restricted by statute. Certain other material, such as copyrighted 
material, is not placed on the Internet and will be publicly available 
only in hard copy form. Publicly available docket materials are 
available either electronically in RME or in the official file which is 
available 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 am and 4:30 pm 
weekdays except for legal holidays. Contact the person listed in the 
FOR FURTHER INFORMATION CONTACT paragraph below or Mr. Bill Deese at 
(214) 665-7253 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 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: Guy R. Donaldson, Air Planning Section 
(6PD-L), Environmental Protection Agency, Region 6, 1445 Ross Avenue, 
Suite 700, Dallas, Texas 75202-2733, telephone (214) 665-7242 fax 
number 214-665-7263; e-mail address donaldson.guy@epa.gov.

SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,'' 
``us,'' or ``our'' is used, we mean the EPA.

Table of Contents

I. Background
    A. What Are the Actions Being Proposed Here?
    B. Why Control Ozone?
    C. What Does the Currently Approved SIP for HGB Contain?
    D. What Revisions to State Implementation Plan Are Being 
Considered Here?
    E. What General Criteria Must These Revisions Meet To Be 
Approvable?
II. Evaluation
    A. One Hour Attainment Demonstration
    1. What Modeling Approaches Were Used for This Attainment 
Demonstration?
    2. What Is a Photochemical Grid Model?
    3. What Episode Did Texas Choose To Model?
    4. How Well Did the Model perform?
    5. What Did the Results of Modeling Routine Emissions Show?
    6. What Did the Results of the Emission Event Modeling Show?
    7. How Did Texas Handle Questions About Emission Estimates?
    8. What Actions Are Being Taken To Improve Emissions Estimates 
of HRVOCs?
    9. What About Estimates of Less-Reactive VOC Emissions?

[[Page 58120]]

    10. What Additional Evidence Did Texas Provide?
    11. Is the One-Hour Attainment Demonstration Approvable?
    B. New Control Measures
    1. What Are the New Control Measures in these SIP revisions?
    2. What Are the Annual Cap and Short-Term Limit on HRVOC 
Emissions?
    3. How Are Annual Cap and Short-Term Limits Related?
    4. Can Reductions in Less-Reactive VOCs Be Made Instead of 
Reductions in HRVOCs?
    5. What Estimates of Flare Efficiency Are Made in the SIP 
Revision?
    6. How Has the Texas Leak Detection and Repair Program Been 
Strengthened?
    7. How Have the Benefits of the Leak Detection and Repair 
Program Been Projected?
    8. What Are the Requirements for Portable Gasoline Containers?
    C. Revised Control Measures
    1. What Control Measures Have Been Revised or Repealed?
    D. Reasonably Available Control Measures
    1. What Are the RACM Requirements?
    2. How Has Texas Insured With This Plan Revision That all RACM 
are Being Implemented?
    E. Section 110(l) Analysis
    1. What Does Section 110(l) Require?
    2. How Has Texas Shown These Revisions Do Not Interfere With 
Attainment of the 8-Hour Standard?
    3. What About Possible Interference With the 1-Hour Ozone 
Standard?
    4. How Has Texas Shown These Revisions do not Interfere With 
Rate of Progress?
    5. Do These Revisions Interfere With Attainment of other 
Standards Besides Ozone?
    6. Do the Revisions Interfere With any Other Applicable 
Requirements of the Act?
    F. Enforceable Commitments
    1. What Is an Enforceable Commitment?
    2. What Were the Enforceable Commitments in the 2001 Approved 
SIP and Have They Been Fulfilled?
    G. Motor Vehicle Emissions Budgets
    1. What Is a Motor Vehicle Emissions Budget and Why Is it 
Important?
    2. What Are the Motor Vehicle Emissions Budgets Being Proposed 
for Approval?
III. Statutory and Executive Order Reviews

I. Background

A. What Are the Actions Being Proposed Here?

    EPA is proposing to approve the following revisions to the approved 
1-hour ozone attainment plan for the HGB area:
     TCEQ's revised demonstration, submitted December 2004, 
that the 1-hour ozone standard will be achieved in 2007.
     The revised motor vehicle emissions budgets associated 
with the revised attainment demonstration.
     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 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 are as effective in reducing ozone levels.
     Revisions to the industrial NOX rules submitted 
January 2003, which included several miscellaneous changes and the 
reduction in stringency from a nominal 90% to 80% control.
     Revisions to the Texas Inspection and Maintenance (I/M) 
rules that drop three counties from the I/M program. In addition, 
several miscellaneous changes are proposed for approval.
     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 
(VMEP).
    To replace the above measures being repealed or relaxed, Texas has 
adopted the following new control measures:
     Annual Cap on HRVOC emissions.
     Hourly (short-term) limit on HRVOC emissions.
     Improved requirements for HRVOC fugitive emissions.
     Requirements for Portable Gasoline containers.

Separately, EPA has proposed or is proposing to approve the newly 
adopted measures. Comments on the proposed approval of the new control 
measures should be directed to these separate Federal Register actions. 
The actions addressed in this rulemaking in conjunction with the new 
HRVOC rules, if approved, will provide for timely attainment as 
demonstrated through the modeling analysis. In addition, 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 this Act. (Section 110(l) 
demonstration).

B. Why Control Ozone?

    Inhaling even low levels of ozone can trigger a variety of health 
problems including chest pains, coughing, nausea, throat irritation, 
and congestion. It can also worsen bronchitis and asthma and reduce 
lung capacity. EPA has established National Ambient Air Quality 
Standards (NAAQS) for ozone. The standard of 0.12 ppm averaged over a 
1-hour period was adopted in 1979. In July 1997, EPA adopted a revised 
standard of 0.08 ppm averaged over an 8-hour period. In the Phase I 
Implementation Rule (April 30, 2005, 69 FR 23951) for the 8-hour 
standard, EPA provided for revocation of the 1-hour standard for most 
areas including HGB on June 15, 2005. Also, EPA established anti-
backsliding provisions to insure that areas maintain the progress 
expected under the requirements of the 1-hour standard as areas 
transition to developing programs to meet the 8-hour standard.

C. What Does the Currently Approved SIP for HGB Contain?

    On November 14, 2001, EPA approved the 1-hour ozone attainment plan 
for the HGB nonattainment area. This plan relied primarily on 
reductions in emissions of NOX to project attainment. The 
plan included a wide variety of controls on NOX emissions 
including an approximately 90% reduction in industrial NOX 
emissions, vehicle inspection and maintenance in eight counties, and 
the Texas Emission Reduction Program (TERP). The plan, however, did not 
contain sufficient adopted control measures as needed to demonstrate 
attainment. Because the State had adopted NOX measures more 
stringent than any where else in the country and was unable to identify 
specific NOX measures by which to achieve all of the needed 
emission reductions, the State included an enforceable commitment to 
adopt rules to achieve the 56 tpd of additional emission reductions 
which were necessary to demonstrate attainment. The additional measures 
were to be adopted in two phases; measures to achieve 25% of the needed 
reductions were to be adopted by December 2002 with measures to achieve 
the remaining emission reductions to be adopted by May 2004. In 
addition, Texas committed to perform a mid-course review, evaluating 
the modeling, inventory data and other tools and assumptions used to 
develop the plan and make adjustments to the plan to provide for timely 
and cost effective attainment. If, based on the mid-course review, more 
or fewer NOX reductions were necessary, Texas committed to 
provide the revised analysis to EPA for review.
    Texas, however, was sued in State court on its plan for the Houston 
area. The litigants alleged that the controls on industrial 
NOX emissions of approximately 90% would not be effective 
and that instead the State should be controlling releases of HRVOCs. 
Texas entered into a settlement agreement with the litigants whereby 
one facet of the mid-course

[[Page 58121]]

review was accelerated to determine if the point source NOX 
controls could be relaxed and replaced with controls on HRVOCs. This 
study and any consequent rule changes were to be completed by December 
2002.

D. What Revisions to the State Implementation Plan Are Being Considered 
Here?

    The following submissions which impact the HGB attainment plan are 
being considered :
    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 relaxed and controls on 
HRVOCs could be substituted. Based on the study, the commission adopted 
relaxed controls on NOX emissions from industrial sources 
and 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 TERP emission reductions would be sufficient to 
achieve the 25% of the NOX reductions needed to demonstrate 
attainment (i.e., about 14 tpd).
    October 16, 2003: This submission delayed compliance for the I/M 
program in Chambers, Liberty and Waller Counties. (RME R06-OAR-2005-TX-
0035)
    October 6, 2004: This submission repealed the I/M program in 
Chambers, Liberty and Waller Counties.(RME 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 was submitted to meet 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 (Docket R06-
OAR-2005-TX-0013), the speed limit strategy, the voluntary mobile 
emissions program (VMEP) and the commitment to achieve NOX 
reductions reductions beyond the initial 25% provided in January 2003 
(i.e., revoked the State's commitment to achieve 42 tpd of the 
NOX reductions that were included in the enforceable 
commitment as part of the prior attainment demonstration).

E. What General Criteria Must These Revisions Meet To Be Approvable?

    To be approved, the revisions to the attainment demonstration must 
meet several requirements. First, the State submission must demonstrate 
that the revised plan, as a whole, will result in attainment of the 1-
hour as expeditiously as practicable but no later than 2007. This is 
necessary, even though the 1-hour standard was revoked on June 15, 
2005, because the approved SIP commits the State to adopt 56 tons/day 
of additional NOX reductions unless, based on the mid-course 
review analysis, the area can show attainment of the 1-hour standard by 
2007 with a different mix of emission reductions.\1\ In Section II.A. 
we discuss TCEQ's revised 1-hour attainment demonstration. Second, the 
measures in the revised control strategy must meet the requirements for 
being creditable under the Clean Air Act and must be permanent, 
surplus, quantifiable and enforceable and achieve the necessary amount 
of reductions. The new and revised measures are discussed in Section 
II.B. and II.C. Some of these control measures have been or are being 
reviewed in separately proposed rules. Before the revisions to the 
attainment plan can be finally approved, all of the control measures 
relied on in the attainment plan must also be approved. Third, the 
State must show that the revised control strategy includes all 
reasonably available control measures (RACM). This showing is discussed 
in Section II.D. Fourth, the State must show, as required by section 
110(l) of the Clean Air Act, that the revisions to the plan will not 
interfere with attainment or reasonable further progress or any other 
applicable requirement of the Act. Compliance with 110(l) is discussed 
in Section II.E. Finally, the State must show that it has met all of 
the enforceable commitments contained in the approved SIP. (Instead of 
meeting the enforceable commitment to achieve the remaining 42 tpd 
NOX reductions, the State has adopted controls on HRVOCs and 
submitted modeling to demonstrate that the 42 tons/day of 
NOX reductions is not necessary for the HGB area to attain 
by November 2007.) Enforceable commitments are discussed in Section 
II.F.

II. Evaluation

A. One Hour Attainment Demonstration

1. What Modeling Approaches Were Used for This 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 by 2007. Also, as allowed 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.
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    \1\ In addition, EPA has retained the 1-hour attainment 
demonstration requirement as an applicable requirement under the 
Phase I rules antibacksliding provisions. See 40 CFR 51.900(f).
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    The SIP revision actually relies on two sets of modeling analyses. 
First, the SIP 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 to 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).
2. What Is a Photochemical Grid Model?
    Photochemical grid models are the state-of-the-art method for 
predicting the effectiveness of control strategies in reducing ozone 
levels. The model uses a three-dimensional grid to represent conditions 
in the area of interest. In this case, TCEQ has developed a grid system 
that stretches from beyond Austin to the west, to Georgia to the east, 
to Nebraska to the north and into the Gulf of Mexico to the south. The 
model uses nested grid cells of 36 km on the outer portions, 12 km in 
east Texas and portions of nearby States and a 4 kilometer grid cell 
covering the HGB and Beaumont Port Arthur (BPA) areas. For more 
information on the modeling domain, please see the TSD. The model 
simulates the movement of air and emissions into and out of the three-
dimensional grid cells (advection and

[[Page 58122]]

dispersion); mixes pollutants upward and downward among layers; injects 
new emissions from sources such as point, area, mobile (both on-road 
and nonroad), and biogenic into each cell; and uses chemical reaction 
equations to calculate ozone concentrations based on the concentration 
of ozone precursors and incoming solar radiation within each cell.
    Air quality planners choose an historical episode of high ozone 
levels to apply the model. Running the model requires large amounts of 
data inputs regarding the emissions and meteorological conditions 
during an episode. Modeling to duplicate conditions during an 
historical episode is referred to as the base case modeling and is used 
to verify that the model system can predict the historical ozone levels 
with an acceptable degree of accuracy. If the model can predict the 
ozone levels in the base case, it can then be used to project the 
response of future ozone levels to proposed emission control 
strategies.
3. What Episode Did Texas Choose To Model?
    Texas chose an historical episode, August 19-September 6, 2000, 
that encompassed the time period of the Texas Air Quality Study (TxAQS) 
2000. During this study, researchers from around the country 
participated in an intensive study of ozone formation in the HGB area, 
collecting additional meteorological and chemical data. This study has 
provided a wealth of information to test the assumptions in the model. 
EPA believes that the extended episode from August 19-September 6, 
2000, is an acceptable episode for development of the 1-hour attainment 
plan. It encompasses 13 exceedance days and contains a variety of 
meteorological conditions which resulted in high concentrations of 
ozone in the area as measured on both a 1-hour and 8-hour basis.
4. How Well did the Model Perform?
    Model performance is a term used to describe how well the model 
predicts the ozone levels in an historical episode. As models have to 
make numerous simplifying assumptions and the system being modeled is 
very complex, model predictions will never be perfect. EPA has 
developed various diagnostic, statistical and graphical analyses that 
TCEQ has performed to evaluate the model's performance and determine if 
the model is working adequately to test control strategies. For a 
subset of days, August 25, 26, 29, 30, 31, September 1-4 and 6, TCEQ 
deemed the model's performance adequate for control strategy 
development to address routine emissions. EPA agrees that the overall 
model performance is adequate but notes that the model tends to under-
predict on high days and over-predict on low days raising some 
uncertainty in the control strategy modeling. At least part of the 
under prediction has been attributed to non-routine emissions not 
captured in the modeling. This is discussed further in the section on 
alternative design values. It is also worth noting that, to achieve 
adequate performance, TCEQ adjusted the amount of HRVOC emissions in 
the model above the reported emission inventory values based on ambient 
measurements which demonstrated that reported HRVOC emissions were 
underestimated. This adjustment is discussed in more detail in later 
sections.
5. What Did the Results of the Modeling of Routine Emissions Show?
    The results of modeling the revised control strategy are shown in 
Table 1.

----------------------------------------------------------------------------------------------------------------
                                                                                                  Modeled peak
                       Episode day                           Measured peak      Modeled peak      (future case
                                                                                 (base case)          \2\)
----------------------------------------------------------------------------------------------------------------
August 25................................................              194               156.5             121.6
August 26................................................              140               149.4             113.6
August 29................................................              146.7             151.2             113.6
August 30................................................              200.5             137.2             122.5
August 31................................................              175.5             173.0             147.6
September 1..............................................              163.7             136.7             119.5
September 2..............................................              125.5             152.7             128.6
September 3..............................................              127.2             139.3             115.0
September 4..............................................              145.0             158.0             125.2
September 6..............................................              156.0             152.9             125.1
----------------------------------------------------------------------------------------------------------------

    Table 1 shows that on all of the days except August 31, the modeled 
control strategy was predicted to bring the area under or very near the 
one-hour standard of 125 ppb. The modeling, however, incorporates only 
routine emissions in the future case and reported non-routine emissions 
in the base case. As will be discussed in more detail in later 
sections, TCEQ believes that large non-routine emission events not 
included in the modeling also contribute to high ozone levels in the 
HGB area. These non-routine emission events explain, in part, the 
model's under-prediction on several days such as August 25th, 30th, and 
September 1st.
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    \2\ These values also do not include the impact of wildfires as 
discussed in the WOE section.
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    As discussed in the weight of evidence section regarding 
alternative design values, the TCEQ believes that without the influence 
of emission events, an alternative design value of 144 ppb can be 
estimated. If 144 ppb is a reasonable representation of the area's 
ozone levels due to routine emissions, then the modeling results in 
Table 1 indicate sufficient reductions in ozone levels due to routine 
events. In addition to the modeling results and the alternative design 
value approach which is explained later in this notice, TCEQ has 
presented other evidence to demonstrate that attainment will be 
reached. These additional demonstrations are included in the weight of 
evidence section.
    To address the part of the ozone levels due to non-routine 
emissions, TCEQ established a short term limit of 1200 lb/hr on 
emissions of HRVOCs. The development of this limit is discussed in the 
next section on emission event modeling. The purpose of this limit is 
to reduce the frequency of non-routine emission events sufficiently so 
that emission events impacting peak ozone levels will be reduced in 
frequency to less than 1 event per year and thus will not impact 
attainment of the 1-hour standard.
    We recognize that there is considerable uncertainty regarding the 
impact of emission events on peak ozone. As we discuss in the next 
section on emission event modeling, the project H13 study seems to 
indicate a smaller impact of emission events on peak ozone levels than 
the alternative design value approach. The projected smaller

[[Page 58123]]

impact could stem from the following reasons. First, the H13 study 
looked at the impact of emission releases after the institution of 
NOX controls, whereas the alternative design value analysis 
performed by TCEQ is based on historic data before the institution of 
controls. Thus, the impact of emission events in the past is likely to 
be larger than events in the future when there is less NOX 
with which to react. Second, the frequency of events was based only on 
detected and reported events. Past monitoring and reporting techniques 
may not have detected all events. The improved HRVOC reporting rules 
should help address this possible problem. Finally, project H13's 
assumptions regarding the frequency of events looked only at events 
occurring at the most sensitive times and location. Larger events 
occurring at slightly less sensitive times and locations could also be 
impacting peak ozone. On the other hand, it is likely that the 
alternative design value approach overstates the impact of emission 
events. Some of the rapid rises in monitored ozone that are filtered 
out in the alternative design value approach could be caused by narrow 
continuous plumes of ozone sweeping across a monitor as winds shift 
direction. Weighing the available information, EPA believes that the 
occurrence of emission events in the HGB area that are not included in 
the model contribute at least in part to the model's under prediction 
of some measured ozone levels. The short-term limit will address these 
non-routine emission events. In addition, the controls on routine 
emissions will provide the reductions in the ozone due to routine 
emissions necessary to reach attainment. In addition, Texas has 
considered other weight of evidence information indicating there will 
be more improvement in air quality than can be expected demonstrated by 
the modeling of routine emissions.
6. What Did the Results of the Emission Event Modeling Show?
    Traditionally ozone control plans have been based on the assumption 
that emissions for an area do not change significantly from day to day 
and differences in pollution levels are caused by changes in the 
meteorological conditions between days. This assumption has been 
reexamined for the Houston area because of the number of non-routine 
emissions that are reported in the Houston area from the refining and 
petrochemical industry.
    The project H13 report, ``Variable Industrial VOC Emissions and 
Their Impact on Ozone Formation in the Houston Galveston Area,'' April 
16, 2004, looked at the potential impact of emission releases in the 
area. It determined, by examining the TCEQ emission events data base 
and records of emissions from sources with monitors on flares and 
cooling towers, that ``variability in HRVOC emissions from point 
sources is significant and due to both variability in continuous 
emissions and discrete emission events.'' The area wide variability had 
the following characteristics:2-3 times per month HRVOC emissions 
variability > 10,000 lbs/hour,2-3 times per month HRVOC emissions 
variability 5,000-10,000 lbs/hour, daily HRVOC emissions variability > 
100 lbs/hour.
    Based on the above findings, the researchers then examined the 
impact that emissions variability could have on peak ozone levels by 
modeling the impact of emission events of various sizes at various 
locations and times. It was determined that an event of 1,000 lbs in 
the most sensitive area and during the most sensitive time could have a 
1-2 ppb impact on the peak ozone level within the fine grid modeling 
domain. Larger events would have correspondingly larger impacts on 
ozone levels. A 10,000 lb release at the most sensitive place could 
have a 10-20 ppb impact on ozone levels.
    The study, based on assumptions regarding the frequency of ozone 
conducive weather conditions, the time window most sensitive to 
releases and the location of most sensitive releases, presented the 
results of a Monte Carlo simulation to estimate the probability and 
expected magnitude of emission events that would impact peak ozone 
levels. The report states that if no actions were taken to reduce 
emissions variability, an air quality plan should anticipate that at 
least one event per year of 1,000 lbs would happen at the right time 
and the right place to impact peak ozone. Based on this finding, TCEQ 
adopted a short-term limit on HRVOC emissions designed to reduce the 
magnitude and frequency of emissions events. This is not to say that a 
1-2 ppb increase in ozone is not significant, but that with the short 
term limit, the occurrence of non-routine events at the times and 
places to impact peak ozone will be diminished sufficiently as not to 
impact attainment with the 1-hour ozone standard. Because facilities 
would be expected to take action to avoid events of 1,200 lbs/hr, the 
frequency of such events in the future will be lower than in the past 
and therefore less than 1 event per year impacting peak ozone should be 
expected. As discussed, some non-routine emissions, in the past, may 
not have been detected or reported in which case the actual frequency 
of events impacting peak ozone levels may be higher than projected in 
project H13, which as discussed previously, would help explain the 
under-prediction in the routine modeling. The improved monitoring 
requirements in chapter 115 should serve to prevent undetected HRVOC 
releases in the future and the specter of enforcement will cause 
facilities to take measures to prevent emission events. This is further 
discussed in the section on the short term and long term cap.
7. How Did Texas Handle Questions About Emission Estimates?
    TCEQ has followed acceptable procedures for the development of the 
base case inventory, following or building upon EPA guidance. Despite 
these efforts, one of the findings of the TexAQS 2000 study was that 
observed concentrations of certain compounds, especially light olefins 
such as ethylene and propylene, were much larger than represented in 
the reported emission inventory. This conclusion has been reviewed and 
documented in numerous scientific journals. For more information on 
these studies see the TSD.
    Emissions of these compounds principally come from the 
petrochemical industry. While it is clear that the reported emissions 
are too low, the ambient data does not show, however, which types of 
facilities and equipment are the source of the underestimated 
emissions. Various methods have been attempted to estimate the actual 
emissions of VOCs in the HGB area based on the available ambient 
measurements. TCEQ decided to use data from aircraft flights which 
indicated NOX emissions were similar to VOC emissions when 
considered on a molar basis. Therefore, TCEQ adjusted the molar 
emission rate of HRVOC emissions at each facility to match the 
NOX emission rate. This adjustment is more fully described 
in Chapter 3 of the SIP revision. The adjustment had the effect of 
substantially increasing the level of HRVOC emissions in the modeled 
emissions inventory. Prior to adjusting the inventory, the model did 
not perform well. Model performance was improved after the adjustment. 
The adjusted inventory became the basis for achieving acceptable model 
performance and for the control strategy development.
    Clearly, this type of across-the-board adjustment of emissions is 
not the preferable way to estimate emissions and makes control strategy 
targeting and development difficult. Unfortunately, using established 
methods for estimating source emissions has been

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demonstrated to be inaccurate. As support for their adjustment 
approach, TCEQ points out the amount of emissions added to the 
inventory is corroborated by a study conducted by Environ ATop Down 
Evaluation of the Houston Emissions Inventory Using Inverse Modeling'' 
(Yarwood et al., 2003) which indicated that approximately the right 
amount of reactivity had been added to the model and that further 
adjustment was not warranted under the then-current model formulation.
    EPA believes that the approach Texas has taken to estimate the 
inventory of HRVOCs is acceptable given the information that is 
available. This conclusion is supported by the available aircraft data 
and Environ inverse modeling study. Clearly, this is an area that 
should be improved as the State develops future SIP revisions.
8. What Actions Are Being Taken To Improve the Emissions Estimates of 
HRVOCs?
    It was the consensus at a conference of emissions inventory experts 
held in Clear Lake, Texas in 2001, that the errors in the inventory 
were most likely from errors in the estimates of emissions from cooling 
towers, flares, fugitive emissions and start-up, shutdown and 
malfunction events. Texas has moved forward to improve the inventory of 
HRVOCs in all of these areas by requiring monitoring of cooling towers, 
flares, pressure relief devices and process vents in HRVOC service. 
This source monitoring, which will be in place by the end of 2006, 
should dramatically reduce the amount of error in the HRVOC inventory 
by more directly measuring both continuous emissions and emissions 
events. In addition, for all VOCs, Texas is now requiring that 
correlation equations be used for the estimation of fugitive emissions. 
This will reduce the amount of error in fugitive emission estimates.
9. What About Estimates of Less-Reactive VOC Emissions?
    Texas elected to adjust the reported emission rates of only HRVOCs. 
Other less-reactive chemicals are also released from flares, cooling 
towers, fugitive sources and during start up/shutdown and malfunction 
events and traditional emissions estimation techniques for less-
reactive VOCs are the same as those for HRVOC. Thus, it is reasonable 
to suspect that these chemicals are also under-represented in the 
inventory. If these chemicals are under-represented in the inventory, 
the degree of underestimation may be less than for HRVOCs. One reason 
is that the processes that emit HRVOCs, such as ethylene plants, are 
often under very high pressures and this may increase the degree of 
underestimation more than would occur for emissions in lower pressure 
processes as one would expect leaks under higher pressures would tend 
to release a greater mass of emissions than lower pressure leaks. Also, 
many less-reactive VOCs are much lower in volatility than the HRVOCs 
which could also serve to reduce the amount of emissions 
underestimation.
    There is some evidence from ambient measurements that the less-
reactive chemicals are underestimated in the emission inventory, but 
there are not yet the number of peer reviewed studies regarding these 
other VOCs that exist for HRVOCs making determination of appropriate 
adjustment factors problematic. Therefore, Texas chose not to adjust 
the reported inventory for the less-reactiveVOCs for the attainment 
demonstration modeling because of the lack of information regarding the 
appropriate level of emissions. TCEQ did conduct a study of ambient 
data, referred to in the SIP revision, indicating that emissions might 
be underestimated by a factor of 4.8. Based on this study, Texas 
performed a sensitivity run with the model to evaluate the impact 
potential errors in less-reactive VOC emissions might have on projected 
attainment. This sensitivity analysis indicated that the addition of 
less-reactive VOCs using a factor of 4.8 could have an impact of 2-29 
ppb on the peak ozone depending on the day. The performance of the 
model, however, was slightly worsened by the addition of the less-
reactive VOCs indicating that possibly too much reactivity had been 
added. Other analyses performed by the University of North Carolina 
(Role of Modeling Assumptions in Mid-Course Review, HARC 12.2004.8HRB, 
2005) adjusting only fugitive emissions of less-reactive VOCs by lower 
factors indicated no more than a 0.5 ppb increase in ozone levels. The 
main differences between the analyses were the assumptions regarding 
the amount of additional less-reactive VOCs and the amount of HRVOCs in 
the model.
    EPA is proposing to accept the attainment demonstration based on 
TCEQ's approach to less reactive VOCs, because of the uncertainty on 
what adjustments might be appropriate and what impact those adjustments 
might have on the model. We understand that TCEQ is continuing to 
evaluate ambient data to determine what adjustments to the inventory 
might be appropriate. Texas has also undertaken a stakeholder process 
to identify additional ways to improve the emissions inventory. This 
stakeholder process will be vital to the improvement of future SIP 
revisions. EPA expects that future SIPs revisions will be based on 
improved emissions inventories of both less-reactive VOCs and HRVOCs. 
We note that the move to require the correlation equations for the 
estimation of less-reactive VOC will serve to improve the estimate of 
fugitive emissions. Improvements to the emission estimates for cooling 
towers and flares in less reactive VOC service should also be 
considered. Roles should also be found for emerging remote sensing 
technologies that have been shown to detect leaks from sources which 
have not been traditionally considered such as barge hatches and 
fittings on floating roof storage tanks.
10. What Additional Evidence Did Texas Provide?
    The EPA's 1996 guidance entitled ``Guidance on Use of Modeled 
Results to Demonstrate Attainment of the Ozone NAAQS'' allows for the 
use of alternative analyses, called weight-of-evidence (WOE), to 
provide additional evidence that the proposed control strategy, 
although not modeling attainment, is nonetheless expected to achieve 
attainment by the attainment date. More specifically, the intent of 
this guidance was to be cognizant of the ozone NAAQS, which allows for 
the occurrence of some exceedances and to consider potential 
uncertainty in the modeling system. Thus, even though the specific 
control strategy modeling may predict some areas to be above the NAAQS, 
this does not necessarily mean that with the implementation of the 
control strategy, monitored attainment will not be achieved. As with 
other predictive tools, there are inherent uncertainties associated 
with modeling and its results. For example, there are uncertainties in 
the meteorological and emissions inputs and in the methodology used to 
assess the severity of an exceedance at individual sites. The EPA's 
guidance recognizes these limitations, and provides a means for 
considering other evidence to help assess whether attainment of the 
NAAQS is likely.
    Since the future control case modeling in the Texas SIP revision 
predicts some areas still exceeding the ozone NAAQS, the TCEQ elected 
to supplement the control strategy modeling with WOE analyses. Texas 
submitted the following analysis as WOE: August 31st rare meteorology; 
additional reductions that were not modeled; comprehensive ozone 
metrics and ambient trends; alternative design value and addressing 
short-term excursions; and unusual wildfire

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activity. Each of these is discussed below.

August 31st Rare Meteorology

    A combination of unusual meteorological conditions, extremely high 
temperatures and winds from the west, occurred on August 31, 2005. The 
record high temperatures recorded during the August 30-September 5, 
2000 period, with several days of maximum temperature >=104[deg]F 
(40[deg]C), have occurred in this geographic area only once before in 
the previous 57 years. On August 31st, the Houston Intercontinental 
Airport observed its highest temperature ever recorded in the month of 
August. High temperatures throughout the region led to higher than 
normal estimated biogenic emissions as the calculation of biogenic 
emissions is a strong function of temperature. Texas calculated that 
biogenic emissions within the HGB area were approximately 400 tons/day 
higher on August 31st than on August 25th which had more moderate 
temperatures. The elevated biogenic emissions in rural areas west of 
Houston were also high and, because of somewhat atypical winds from the 
west, available for transport into HGB. Texas used the source 
apportionment tool (OSAT) to analyze the contributing emissions to high 
ozone. The OSAT tool indicated that on the 31st, 78 ppb of the peak 
ozone could be attributed to biogenics as compared to 24 ppb that could 
be attributed to biogenics on the 25th. Other days of the episode also 
had high temperatures but only when combined with the west winds did 
the unusual impact of biogenics result. Texas points out that winds 
from the west are not typical of the days that have high ozone in 
Houston which usually occur on days with a flow reversal due to the 
land sea breeze effect.
    EPA agrees that the meteorological conditions on August 31st, which 
combined record high temperatures and winds from the west, were not 
typical of the conditions that lead to high ozone in the HGB area. The 
higher than normal biogenic emissions and winds from the west appear to 
have caused the 31st to be a day that did not respond well to the 
adopted control strategy which is weighted toward control of point 
sources that are predominant in eastern Harris County. This strategy 
has been effective in reducing ozone levels on other days of the 
episode. On the 31st, it appears much of the elevated ozone resulted 
from the increased biogenic emissions mixing with the NOX 
emissions present in the western portion of the HGB area. In this 
portion of the area, NOX emissions are primarily from on- 
and off-road mobile sources. To control ozone levels on days with 
routine conditions similar to August 31st would require substantial 
additional controls on mobile and area sources beyond the levels in the 
current strategy. But because the conditions on the 31st are atypical, 
we believe the HGB area can attain and a shift in strategy is not 
warranted.
    EPA's rules at 40 CFR 50, Appendix I permit the Regional 
Administrator to exclude values caused by stratospheric ozone intrusion 
or natural events in determining whether a NAAQS has been exceeded or 
violated. Additionally, EPA's long-standing policy and guidance on the 
handling of air quality data affected by exceptional or natural events 
permits special consideration to be given to recorded air quality 
measurements that are affected by unusual events under certain 
circumstances. See, e.g., ``Guidance on the Identification and Use of 
Air Quality Data Affected by Exceptional Events (July 1986)''. However, 
this guidance and other guidance distinguish between those types of 
events which directly produce emissions of a pollutant or its 
precursors and meteorological conditions that may affect concentrations 
of a pollutant emitted by sources. In particular, EPA guidance provides 
that no consideration is given in determining whether the NAAQS are 
exceeded or violated for such things as inversions, stagnation of air 
masses, high temperatures or lack of rainfall. This language has 
recently been codified in an amendment to section 319 of the Clean Air 
Act by P.L. 109-59 [SAFETEA]. However, a reasonable distinction may be 
drawn between the determination of whether NAAQS are exceeded or 
violated during times when such meteorological conditions exist and the 
meteorological and emissions data sets used in prospective 
demonstrations of attainment. In the latter, our policy has been for 
States to examine the typical conditions that lead to high ozone when 
modeling to determine whether their control strategies are sufficient 
to provide for attainment and maintenance of NAAQS. (U.S. EPA, (1996), 
``Guidance on Use of Modeled Results to Demonstrate Attainment of the 
Ozone NAAQS'', EPA-454/B-95-007.) In this case, the combination of 
conditions on the 31st are not typical and, in fact are quite rare. 
Therefore, EPA does not believe a shift in control strategy is 
warranted to address the unusual conditions on August 31st that are 
expected to occur so infrequently as to be unlikely to impact the 
area's ability to attain the NAAQS.

Additional Reductions Not Modeled

    The TCEQ believes potential additional emissions reductions will 
take place as a result of programs which have been and will be 
implemented in the HGB area but which are not reflected in the 
modeling. These reductions are not included in the modeling because, at 
present, these reductions are not quantifiable. Emission reductions 
that were not included in the model should improve the probability of 
HGB achieving attainment of the ozone NAAQS. First, as industries 
improve their monitoring capabilities and reduce their HRVOC emissions, 
the TCEQ anticipates collateral reductions of other VOCs that are 
present in HRVOC streams. For instance, the TCEQ developed regulations 
requiring owner/operator of flares in HRVOC service to install flow-
meters and comply with maximum tip velocity and minimum heat content 
requirements to ensure proper combustion by the flare. The tip velocity 
and heat content requirements apply at all times, not only when the 
flare is combusting HRVOC streams. Because many of these flares are 
also used for non-HRVOC streams, the regulations will often result in a 
reduction of less-reactive VOCs as well. Similarly, TCEQ has improved 
the leak detection and repair program for streams with more than 5% 
HRVOC content. When leaks from streams containing both HRVOCs and less 
reactive VOCs are repaired, other less-reactive VOCs will also be 
reduced. EPA agrees that these collateral reductions are likely to 
occur, but we believe the potential benefit of these unmodeled emission 
reductions has been partially lost because TCEQ allows emission 
reductions of less-reactive VOCs to offset small increases in HRVOCs 
using the Maximum Incremental Reactivity (MIR) scale (see Section 
II.B.4.). It is likely that some of the benefit will be realized 
because we do not expect that many companies will implement the 
additional monitoring of less reactive VOCs that would be necessary to 
establish baselines necessary to participate in the trading program. 
Also, under the TCEQ rules, less reactive fugitive emissions reductions 
cannot be credited toward HRVOC increases so collateral reductions in 
fugitive emissions should be fully realized. Another issue is the 
uncertainty in the less-reactive VOC inventory. As discussed in the 
section on emissions inventory uncertainty, it may be that less-
reactive VOCs are under-represented in the base case

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inventory. Because of uncertainty about the inventory, these collateral 
reductions may not serve to reduce VOC emissions below what was assumed 
in the model. These collateral reductions will serve to reduce the 
degree of any potential under-representation in the inventory and thus 
reduce this area of uncertainty in the attainment demonstration.
    A second program that should result in additional reductions is the 
Environmental Monitoring Response System (EMRS). The TCEQ and the HRVOC 
regulated community have expanded the real-time ambient monitoring 
network of specific VOCs in the HGB area. A primary goal of EMRS is to 
prevent HRVOC emissions from creating situations that may lead to high 
levels of ozone. The near real time monitoring and response built into 
the program, which is further described in the TSD, will provide rapid 
feed back that should help identify and quickly correct the releases 
that can lead to high levels of ozones. EPA believes this added 
scrutiny of ambient VOC levels will result in improved overall program 
effectiveness, and could identify previously unknown sources of 
emissions that could be controlled to further reduce emissions.
    The TCEQ believes that additional reductions will also be achieved 
through its public web-based access to an emission event database 
incorporating lower reportable quantities of VOCs beyond just the 
HRVOCs of most concern. This database puts facility performance 
regarding unauthorized emission releases at the public's fingertips. As 
public awareness of the number and amount of these releases increases, 
industry is expected to respond in a manner similar to its response to 
the Toxics Release Inventory program which has resulted in large 
reductions in Toxic emissions. EPA agrees awareness and documentation 
of these events should prompt industry to begin to evaluate the causes 
of these events and institute an enhanced program to ensure that the 
potential of an event is significantly minimized.
    Texas believes the projected emissions for electric generating 
units outside the nonattainment area are probably too high. The current 
HGB SIP attainment demonstration modeling only excludes from the future 
case emissions projections for units that have formally indicated an 
intent to cease operation or that will be retired/reduced under agreed 
orders. The future projected case modeling inventory may include 
sources that will in fact be retired in (and/or prior to) 2007 as 
newer, more cost effective plants come online as Texas utilities 
continue the transition to a fully deregulated market. If this occurs, 
additional reductions could result which are not accounted for in the 
current SIP because the newer facilities would have lower emission 
rates. EPA agrees that deregulation will encourage the retirement of 
less efficient plants. Some of the benefit of this process may already 
be incorporated in the projections because Texas has projected newly 
permitted units will operate at 75% capacity in its projection of 
future emissions for electric utility emissions. It may be that newly 
permitted plants operate closer to full capacity as less efficient 
plants are curtailed or retired such that overall projected emission 
levels do not decrease as much. Some reductions should still occur 
because the newer plants will be cleaner than the older plants. A 
factor that weighs toward the projections of future emissions outside 
the nonattainment being too low is the findings of a report on 
emissions from offshore facilities too recent to be included in the SIP 
which indicates that projected emissions from these facilities may be 
significantly higher than what was modeled. Considering these factors 
together, EPA believes that NOX emissions outside the 
nonattainment area are slightly if at all less than projected and 
provide little additional evidence the area will attain.
    Texas also believes that NOX emission projections inside 
the nonattainment area are overestimated. Inside the eight county 
nonattainment area, the Mass Emissions Cap and Trade (MECT) program for 
NOX applies. For sources with permits in hand when the first 
cap allocations were established but which had not yet operated, TCEQ 
issued allowances based on the allowable emissions in the permit (so 
called ``allowable allowances''). Allowable allowances are those 
allocated to sources based on permits issued prior to the initiation of 
the MECT program, but not in operation for sufficient time to establish 
a baseline. During the interim period, until a baseline is established, 
sources operate complying with the ``allowable allowances.'' Then, 
based on the actual emissions during the baseline period, the State 
grants ``actual allowances.'' Because typically these facilities are 
not operating at their full allowable rates, but significantly below 
those values, a source will get fewer ``actual allowances'' than the 
``allowable allowances'' it was granted based on the permit. Therefore, 
as these newly permitted facilities establish baselines from which to 
grant ``actual'' allowances, the NOX cap in the HGB will 
decrease overall. The TCEQ examined the 2002 and 2003 permit database 
and found that only 33 to 39 percent of the allowable allowances for 
permitted facilities were used. The modeling was based on the 
``allowable allowances'' because it was not possible to predict how 
much lower the actual allowances will be than allowable allowances. The 
number of allowable allowances is not insignificant. The TCEQ registry 
currently carries 18,658 allowable allowances for 2007 which could 
translate into a potential additional NOX emissions 
reduction beyond what was modeled of up to 31 tpd if current trends for 
the conversion of allowable allowances to actual allowances continue. 
EPA agrees that as allowable allowances are converted to actual 
allowances, actual emissions will be less than the emissions that were 
modeled which should result in greater improvement in air quality than 
projected in the model.
    In summary, EPA believes that TCEQ has provided sufficient evidence 
that NOX emission levels will be lower than those projected 
in the model and thus, air quality improvements should be better than 
predicted by the model. We also believe the reductions that will occur 
due to collateral VOC reductions and brought about by the EMRS system 
and emission events data base will reduce the uncertainty in the model 
due to uncertainty in the VOC inventory.

Comprehensive Ozone Metrics And Ambient Trends

    Based on the ambient data, the 1-hour ozone design values for the 
HGB area have decreased significantly from 260 ppb in 1982 to 175 ppb 
in 2003. Texas used this initial data to estimate a trend that 
demonstrated that attainment of the 1-hour standard would be reached 
sometime after 2020. The area's design value dropped significantly 
during the 1980s, then flattened out during the 1990s, hovering around 
200 ppb. Design values recently have resumed their downward trend and 
are at the lowest values seen in at least the last twenty years. EPA 
notes that the 2004 design value has further decreased to 169 ppb. The 
current trend may be partly due to meteorological conditions in recent 
years, but it is almost certainly accelerated by emission reductions 
made since the 2000 SIP revision. If the design value continues to drop 
at a rate comparable to that seen in the most recent five-year period, 
then attainment would occur sometime around 2010. But the amount of 
emissions reductions is expected to increase each year until 2007 as a 
result of rules adopted in the

[[Page 58127]]

2000 SIP revision and in this SIP revision. Consequently, the design 
values are expected to decrease more rapidly as 2007 approaches. This 
simplistic analysis alone by no means proves the area will attain the 
standard by 2007, but EPA agrees the recent design value trends are 
consistent with reaching attainment by 2007.

Alternative Design Value And Addressing Short-Term Excursions

    As discussed previously, 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 believes the traditional modeling 
does not replicate ozone produced by the sudden sharp increases in 
HRVOC emissions that can occur in the HGB area due to non-routine 
emission releases. TCEQ argues that this technical deficiency provides 
an explanation for why the model's peak simulated ozone concentrations 
were all below the HGB area's design value in 2000. The actual design 
value calculated for the years 1999-2001 was 182 ppb, while base case 
simulated peak ozone concentrations were below 160 ppb on every day but 
August 31st. The TCEQ believes that the influence from short-term 
releases should 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 the influence of 
short-term releases, TCEQ applied Blanchard's technique (Statistical 
Characterization of Transient High Ozone Events Interim Report; 
December 21, 2001) to the 1999-2001 AIRS data. This technique uses a 
threshold of a 40 ppb rise in ozone concentration in 1 hour to 
distinguish between sudden rises in ozone 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. The base case includes seven days 
with modeled peak ozone greater than 144 ppb, so the modeled peaks, in 
fact, correspond well with the (non-SOCI) design value and in fact the 
model may be over-predicting the ozone resulting from routine 
emissions. If the model is over-predicting the ozone due to routine 
emissions in the base case, then it is likely the model is over-
predicting the ozone due to routine emissions in the future case 
projections providing additional evidence that the control strategy 
will sufficiently reduce the ozone from routine emissions.
    EPA considers the alternative design value approach one 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 
potential impact of large emission releases on the design value. We are 
not convinced, as yet, 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. Wind shifts are a common occurrence in the 
HGB area and are likely responsible for some of these SOCI events. The 
TCEQ analysis also did not screen out widespread exceedences unlikely 
to be the result of a non-routine event. Still, we agree that emission 
events do impact the design value to a degree that is difficult to 
quantify. 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 as Texas has developed a 
strategy to control both routine and event emissions, thus reducing 
both contributions to the design value.
    Wildfire Activity: In 2000, there was an unusually large amount of 
wildfire activity in Southeast Texas due to drought conditions and 
extreme temperatures in the August-September time frame. This is 
documented in Section 3.7.2 of the SIP that shows that more than 5 
times as many acres burned in 2000 as in any of the other years between 
1999 and 2003. It is not expected the number and scope of fires modeled 
in the current SIP attainment demonstration modeling would be 
reasonably expected in future years. A sensitivity analysis was 
conduct