1. Defining “Significant Impact” from Mobile Sources and Road Dust
By John F. Kowalczyk
Co-Chair WRAP Mobile Source Forum
WRAP Board Meeting
July 24, 2002

2. “Significant Impact” Requirements in Section 309
Determine if Mobile Source Emissions or Road Dust “Contribute Significantly” to Visibility Impairment in any of the 16 Class I areas on the Colorado Plateau based on Current and Projected Levels.

3. Definitions
Mobile Sources include On-Road and Non-Road Engine, Evaporative and Tire and Brake Wear Emissions
Road Dust includes Paved and Unpaved
Analyze Mobile Impacts from Major Urban Areas
Analyze Road Dust Impacts from State/Reservation

4. If Mobile Source are a “Significant Contributor”
Requires State to Restrict Emissions to Projected Lowest Levels
Implement Measures to Achieve “Emissions Budget” and Demonstrate Compliance
Establish Emission Tracking System
Separate from Conformity according to EPA

5. If Road Dust is a “Significant Contributor”
Must Implement “Necessary and Appropriate Emission Management Strategies”

6. Questions “Significant” Not Defined “Areas of State” Not Defined
What to do about Inaccuracies in Modeling Road Dust

7. Mobile Source Forum “Preliminary Recommendations”
Three Alternative Definitions of “Significant”
Evaluate Alternatives against Modeling Results for Realisticness and Reasonableness
Choose Alternative or Revise and make Final Recommendation (Expect by end of Summer)
Consensus on Other Issues

8. Alternative” Significant Contribution” Definitions
Cumulative< 1 DV Significance ~ 0.5 DV Cumulative >1DV Significance ~ DV
Significance ~ 1.0DV
Significance ~0.1 DV

9. Alternative 1 Definition of “Significant”
Two Tier “Significance” Level Based on Cumulative Impact from all 9 States
Cumulative Approach based on some Consistency with PSD/NSR and FLAG Programs

10. Alternative 1 (cont.)
If Cumulative Impact (CI) < 10% of Natural Conditions (NC) for Avg. of 20% Most Impaired Days then Area of State/Reservation Significant is > 5% of NC
If CI > 10% of NC Significant is 1% of NC (Exclude any Signif. Area if in lowest 20% of CI)

11. Alternative 2
Individual Area of State/Reservation Approach (Cumulative Impact not considered)
Based on Impact being Perceptible
Perceptible in range of 0.5 DV to 2.0 DV
Significant threshold 1 Deciview

12. Alternative 3
Individual Area of State/Reservation Approach (Cumulative Impact not considered)
Based on Rule Definition of Significant as “Contributor” to Visibility Impairment not a Sole or Perceptible “Cause” of Impairment
Significant Threshold 1% of Natural Background (about 10% of a Deciview)

13. “Areas of State” for Mobile Source Impact Analysis
Counties Encompassing Urban Areas in 9-State Transport Regions with Populations greater than 250,000
11 Areas
2 in AZ, 3 in CO, 1 in ID, 1 in NM, 2 in OR, and 2 in UT
California and Nevada analyzed separately since electing not to go 309

14. Mobile Source Significance Trigger
Significant in Base Year (2003) and Future Year (2018) then Budget/Tracking Applies
Significant in Base but not Future Year and any pollutant reaches minimum before 2018 then Budget/Tracking Applies (SO2)
Significant in Base but not Future Year and all pollutants continually decrease then Future SIP revision, if needed, to meet Reasonable Progress Provision of Rule

15. Road Dust Significance Trigger
If Road Dust Significant in Base and Future Year than Further Analysis after Expected Improvements to Estimated Dust Emissions/Modeling by EPA/WRAP
If still Significant than Reasonable and Appropriate Control Measures apply through SIP/TIP revision no later than 12/31/08

16. Prelim. Modeling Results - On Road Mobile
Smallest Cumulative Impact in 2018: DV at Mesa Verde NP
Largest Cumulative in 2018 : DV at Zion NP
2018 Nonroad Emission Inventory of Major Visibility Precursors is 2 X of On Road EI

17. Preliminary Modeling Results - Road Dust
Smallest Cumulative Impact in DV at Weminuche Wilderness
Largest Cumulative Impact in DV at Black Canyon of Gunnison NP

18. Conclusions
Need Complete Modeling Results (Nonroad + Areas) for Accurate Determination
Cumulative Mobile likely > 1.0DV
Unclear if any 309 area > 0.1 DV
State Road Dust may be < 0.1 DV
Concern that Future Nonroad Emissions Exceed On Road

19. Mobile Source Emission Trend- Tons/Day NOx, SOx,, PM