Section 170. Procedures for conformity determinations

A. The analyses required under this section shall be based on the latest planning assumptions.

1. All planning assumptions (including, but not limited to, per capita water and sewer use, vehicle miles traveled per capita or per household, trip generation per household, vehicle occupancy, household size, vehicle fleet mix, vehicle ownership, wood stoves per household, and the geographic distribution of population growth) shall be derived from the estimates of current and future population, employment, travel, and congestion most recently approved by the metropolitan planning organization or other agency authorized to make the estimates, where available. The conformity determination shall also be based on the latest assumptions about current and future background concentrations and other federal actions.

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 approved by the metropolitan planning organization or other agency authorized to make the estimates for the urban area.

B. The analyses required under this subsection shall 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, the federal agency may obtain written approval from the appropriate EPA Regional Administrator for a modification or substitution of another technique 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 for use in the preparation or revision of the applicable implementation plan shall be used for the conformity analysis as specified in subdivisions 1 a and 1 b of this subsection.

a. The EPA shall publish in the Federal Register a notice of availability of any new motor vehicle emissions model.

b. A grace period of three months shall apply during which the motor vehicle emissions model previously specified by EPA as the most current version may be used unless EPA announces a longer grace period in the Federal Register. Conformity analyses for which the analysis was begun during the grace period or no more than three months 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 nonmotor 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)" shall 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. The air quality modeling analyses required under this section shall be based on the applicable air quality models, databases, and other requirements specified in Appendix W of 40 CFR Part 51.

D. The analyses required under this subsection shall be based on the total of direct and indirect emissions from the action and shall reflect emission scenarios that are expected to occur under each of the following cases:

1. The attainment year specified in the applicable implementation plan or, if the applicable implementation plan does not specify an attainment year, the latest attainment year possible under the federal Clean Air Act; or

2. The last year for which emissions are projected in the maintenance plan;

3. 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

4. Any year for which the applicable implementation plan specifies an emissions budget.

Historical Notes

Derived from Volume 12, Issue 26, eff. January 1, 1997; amended, Virginia Register Volume 27, Issue 11, eff. March 2, 2011.

Statutory Authority

§ 10.1-1308 of the Code of Virginia.