35 Ill. Adm. Code 255.230
Procedures for Conformity Determinations of General Federal Actions
Section 255
Section 255.230 Procedures
for Conformity Determinations of General Federal Actions
a) The analyses required under this Part must be based on the
latest planning assumptions.
1) All planning assumptions must be derived from the estimates of
population, employment, travel, and congestion most recently approved by the
MPO, regional planning commission 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, shall be developed in
consultation with the regional planning commission, MPO or other agency
authorized to make such estimates for the urban area.
b) The analyses required under this Part 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 USEPA 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. Any modification and
substitution shall be done in consultation with IEPA and USEPA.
1) For motor vehicle emissions, the most current version of the
motor vehicle emissions model specified by USEPA and available for use in the
preparation or revision of SIPs in this State must be used for the conformity
analysis as specified in subsections (b)(1)(A) and (B) of this Section:
A) The USEPA must publish in the Federal Register a notice of
availability of any new motor vehicle emissions model; and
B) A grace period of 3 months shall apply during which the motor
vehicle emissions model previously specified by USEPA 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 USEPA.
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)" as
incorporated by reference in Section 255.160 of this Part 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.
c) Any air quality modeling analyses necessary to demonstrate
conformity shall 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" Part 51 – Requirements for Preparation, Adoption,
and Submittal of Implementation Plans, 40 CFR 51, Appendix W, 61 Fed. Reg.
41837 (August 12, 1996) incorporated by reference in Section 255.160 of this
Part, unless:
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) Any modification of substitution shall be done in consultation
with USEPA.
d) The analyses required under this Part, except Section
255.220(a)(1) of this Part, 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 CAA 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.