United States                                                 EPA420-B-04-007
            Environmental Protection                                          JU-/^z,u o ut uu /
            Agency                                                            June 2004
          Boundary Scenarios for 8-hour Ozone Nonattainment Areas
            Previously Designated as Nonattainment or Maintenance
                          for the 1-hour Ozone Standard

                               Reference Document

Note: The purpose of this reference document is to assist the public in understanding Section
VI.A.2. of EPA's final rule entitled, "Transportation Conformity Rule Amendments for the New
8-hour Ozone and PM2 5 National Ambient Air Quality Standards and Miscellaneous Revisions
for Existing Areas; Transportation  Conformity Rule Amendments: Response to Court Decision
and Additional Rule Changes." The final transportation conformity rule was signed on June  14,
2004. Section VI. of the rule is entitled, "Regional Conformity Tests in 8-hour Ozone Areas  That
Have 1-hour Ozone SIPs."

The generic boundary scenarios described in Section VI. are for 8-hour ozone nonattainment
areas that were also designated nonattainment under the 1-hour ozone air quality standard. These
boundary scenarios are important for applying conformity tests in these  areas. The tests apply for
such areas before motor vehicle emissions budgets from SIPs that address the 8-hour ozone
standard are available for conformity purposes.

Please note that scenarios are determined according to how the entire 8-hour nonattainment area
relates to the entire 1-hour nonattainment or maintenance area(s).

EPA will post more detailed implementation guidance on its transportation conformity Web  site
for conformity determinations in new standard areas, including 8-hour ozone areas with 1-hour
SIP budgets and multi-state/multi-MPO nonattainment areas.

State and local agencies can consult with EPA and DOT field offices to determine which
scenario applies to a given 8-hour nonattainment area.

SCENARIO 1: 8-hour and 1-hour Ozone Boundaries Are Exactly the Same

In this scenario, the 8-hour and 1-hour ozone boundaries cover exactly the same geographical
area.
                                               = 1-hour area boundary

                                               = 8-hour area boundary
                        Scenario 1

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SCENARIO 2: 8-hour Ozone Boundary Is Smaller Than and Within the 1-hour Ozone
Boundary

In this scenario, the 8-hour ozone nonattainment area is smaller than and completely
encompassed by the 1-hour ozone boundary.
                   o
                   Scenario 2
      = 1-hour area boundary
Ci  = 8-hour area boundary
SCENARIO 3: 8-hour Ozone Boundary Is Larger Than the 1-hour Ozone Boundary

In this scenario, the entire 1-hour ozone boundary is completely within a larger 8-hour ozone
nonattainment area.
                                                = 1-hour area boundary
                                                = 8-hour area boundary
                       Scenario 3
SCENARIO 4: 8-hour Ozone Boundary Overlaps With the 1-hour Ozone Boundary

In this scenario, the 8-hour and 1-hour ozone boundaries partially overlap.
                      Scenario 4
                                                 = 1-hour area boundary
                                                 = 8-hour area boundary

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