[Code of Federal Regulations]
[Title 40, Volume 18]
[Revised as of July 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR93.159]

[Page 581-582]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 93--DETERMINING CONFORMITY OF FEDERAL ACTIONS TO STATE OR FEDERAL 
IMPLEMENTATION PLANS--Table of Contents
 
Subpart B--Determining Conformity of General Federal Actions to State or 
                      Federal Implementation Plans
 
Sec. 93.159  Procedures for conformity determinations of general Federal 
actions.

    (a) The analyses required under this subpart must be based on the 
latest planning assumptions.

[[Page 582]]

    (1) All planning assumptions must be derived from the estimates of 
population, employment, travel, and congestion most recently approved by 
the MPO, or other agency authorized to make such estimates, where 
available.
    (2) Any revisions to these estimates used as part of the conformity 
determination, including projected shifts in geographic location or 
level of population, employment, travel, and congestion, must be 
approved by the MPO or other agency authorized to make such estimates 
for the urban area.
    (b) The analyses required under this subpart must be based on the 
latest and most accurate emission estimation techniques available as 
described below, unless such techniques are inappropriate. If such 
techniques are inappropriate and written approval of the EPA Regional 
Administrator is obtained for any modification or substitution, they may 
be modified or another technique substituted on a case-by-case basis or, 
where appropriate, on a generic basis for a specific Federal agency 
program.
    (1) For motor vehicle emissions, the most current version of the 
motor vehicle emissions model specified by EPA and available for use in 
the preparation or revision of SIPs in that State must be used for the 
conformity analysis as specified in paragraphs (b)(1)(i) and (ii) of 
this section:
    (i) The EPA must publish in the Federal Register a notice of 
availability of any new motor vehicle emissions model; and
    (ii) A grace period of 3 months shall apply during which the motor 
vehicle emissions model previously specified by EPA as the most current 
version may be used. Conformity analyses for which the analysis was 
begun during the grace period or no more than 3 years before the Federal 
Register notice of availability of the latest emission model may 
continue to use the previous version of the model specified by EPA.
    (2) For non-motor vehicle sources, including stationary and area 
source emissions, the latest emission factors specified by EPA in the 
``Compilation of Air Pollutant Emission Factors (AP-42)'' \1\ must be 
used for the conformity analysis unless more accurate emission data are 
available, such as actual stack test data from stationary sources which 
are part of the conformity analysis.
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    \1\ Copies may be obtained from the Technical Support Division of 
OAQPS, EPA, MD-14, Research Triangle Park, NC 27711.
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    (c) The air quality modeling analyses required under this subpart 
must be based on the applicable air quality models, data bases, and 
other requirements specified in the most recent version of the 
``Guideline on Air Quality Models (Revised)'' (1986), including 
supplements (EPA publication no. 450/2-78-027R) \2\, unless:
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    \2\ See footnote 1 at Sec. 93.159(b)(2).
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    (1) The guideline techniques are inappropriate, in which case the 
model may be modified or another model substituted on a case-by-case 
basis or, where appropriate, on a generic basis for a specific Federal 
agency program; and
    (2) Written approval of the EPA Regional Administrator is obtained 
for any modification or substitution.
    (d) The analyses required under this subpart, except 
Sec. 93.158(a)(1), must be based on the total of direct and indirect 
emissions from the action and must reflect emission scenarios that are 
expected to occur under each of the following cases:
    (1) The Act mandated attainment year or, if applicable, the farthest 
year for which emissions are projected in the maintenance plan;
    (2) The year during which the total of direct and indirect emissions 
from the action is expected to be the greatest on an annual basis; and
    (3) Any year for which the applicable SIP specifies an emissions 
budget.