Defining

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

• Cumulativelt 1 DV Significance 0.5 DV
  Cumulative gt1DV Significance 0.1 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) lt 10 of Natural
  Conditions (NC) for Avg. of 20 Most Impaired
  Days then Area of State/Reservation Significant
  is gt 5 of NC
• If CI gt 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
  0.28 DV at
  Mesa Verde NP
• Largest Cumulative in 2018
  0.78 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 2018
  0.08 DV at Weminuche Wilderness
• Largest Cumulative Impact in 2018
  0.31 DV at Black Canyon of Gunnison NP

18
Conclusions

• Need Complete Modeling Results (Nonroad Areas)
  for Accurate Determination
• Cumulative Mobile likely gt 1.0DV
• Unclear if any 309 area gt 0.1 DV
• State Road Dust may be lt 0.1 DV
• Concern that Future Nonroad Emissions Exceed On
  Road

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