2015-12-16_GENERAL DOCUMENTS - C1981035 ‎(2)‎

• Permit No: C1981035
• IBM Index Class Name: General Documents
• Doc Date: 12/16/2015
• Doc Name: Air Quality Modeling Analysis by McVehil-Monnett /EPA Brocure EPA Fax Sheet on Particle Pollution
• From: Luke Danielson
• To: DRMS
• Permit Index Doc Type: General Correspondence
• Email Name: RAR
• Email Name: DIH
• Media Type: D
• Archive: No

Discussion of Results
Five scenarios were modeled in this study to encompass different traffic levels, model options,
and unpaved road control factors. These scenarios are:
Scenario A - Year 2014 traffic level, default model settings, 50% unpaved road dust control
Scenario B - Year 2014 traffic level, adjust u* option, 50% unpaved road dust control
Scenario C - Peak traffic level, default model settings, 50% unpaved road dust control
Scenario D - Peak traffic level, adjust u* option, 50% unpaved road dust control
Scenario E - Peak traffic level, adjust u* option, 0% unpaved road dust control
Modeled pollutant impacts are analyzed to determine design concentrations for comparison to
the respective NAAQS. The design concentration for a specific criteria pollutant and averaging
period is based on EPA recommendations presented in Section 7.2.1 of the Guideline on Air
Quality Models9. For 24-hour PMIo impacts using a five-year meteorological dataset, the model
design concentration is the highest sixth -high (H6H) concentration at each receptor. That is,
AERMOD calculates the average 24-hour PMIo concentration at each receptor for every day of
the five-year meteorological dataset, and then provides output files listing the sixth -high
concentration at each receptor. These H6H concentrations are then compared to the 24-hour
PMIo NAAQS of 150 gg/m3.
For all modeled scenarios, the H6H concentrations at the five residents/structures located closest
to the unpaved section of County Road 120 exceed the 24-hour PMIo NAAQS. The other 19
resident/structure locations analyzed show much lower impacts, as they are either located much
further from the road or along the paved section. Figures 3 through 7 present H6H 24-hour PMIo
concentration contours for Scenarios A through E, respectively. The figures also present the
predicted concentrations at the five residents/structures where the impacts exceed the NAAQS.
Figure 8 shows detail of the concentration contours near selected residences for Scenario D. The
concentration ranges for each scenario at the five resident/structure locations are detailed below.
Scenario A (Figure 3)
- H6H impacts range from 246 to 469 gg/m3
Scenario B (Figure 4)
- H6H impacts range from 160 to 280 gg/m3
Scenario C (Figure 5)
- H6H impacts range from 302 to 571 gg/m3
Scenario D (Figure 6)
- H6H impacts range from 195 to 340 gg/m3
Scenario E (Figure 7) -
H6H impacts range from 384 to 679 gg/m3
The adjust u* option used in Scenarios B and D reduces predicted impacts 35-40% below the
respective default setting scenarios, but impacts still range well above the NAAQS. Again, we
would try to gain approval to use the adjust u* option were we performing regulatory modeling
for an industrial client. As expected, no concentrations exceed the NAAQS along the paved
section of the road, reflecting the much lower emissions associated with the paved surface. With
the levels of traffic presented in the Roadrunner TIA, an unpaved road dust control factor of
roughly 75-80% would need to be achieved in order to reduce predicted PMIo impacts at all the
resident/structure locations below the NAAQS. This modeling analysis did not include any
background (i.e., local) traffic counts so the actual control factor needed is likely higher than
9 40 CFR Part 51, Appendix W
9250 East Costilla Avenue 1 Suite 630 1 Greenwood Village, Colorado 80112
303/790-1332 1 Fax [phone]
www.mevehil-monnett.com