UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK, NC 27711 

March 2, 2012 

MEMORANDUM 

SUBJECT: Haul Road Workgroup Final Report Submission to EPA-OAQPS 

FROM: TylerFox,Leadit- -7~J~ Air Quality Modeling Group, C439-01 

TO: Regional Office Modeling Contacts 

OFFICE OF 

AIR QUALITY PLANNING 

AND STANDARDS 

The challenge of modeling the emissions and associated air quality impacts of haul roads 

has been a particularly vexing problem for the dispersion modeling community. There is a large 

degree of uncertainty in the magnitude of these fugitive dust emissions and subsequently in the 

modeled estimates at near-source receptor locations. At the 2009 Regional, State, and Local 

Modelers' Workshop, EPA held an interactive session on best modeling practices of haul roads 

that was chaired by Randy Robinson, USEPA Region 5, and Mick Daye, USEPA Region 7 to 

open up a constructive dialog throughout the regulatory dispersion modeling community on the 

challenges of characterizing and appropriately addressing the haul road fugitive emissions in a 

compliance demonstration project. Following this 2009 Workshop, the Haul Road Workgroup 

was formed with a collection of federal, state, and local government dispersion modelers. The 

goal of this Workgroup was to examine and better understand haul road characterization issues 

and recommend a modeling methodology back to the broader dispersion modeling community. 

The Workgroup decided to focus on the air quality modeling aspects and not address the fugitive 

dust emissions factor issues. 

A report out of the Haul Road Workgroup was presented at the 2010 Regional, State, and 

Local Modelers' Workshop. Along with discussion amongst the regulatory dispersion modelers 

in attendance at the 2010 Workshop, feedback and comments were solicited and accepted on the 

recommendations of the Workgroup throughout 2010 and the first half of 2011. An update 

presentation on the Workgroup was given at the 2011 Regional, State, and Local Modelers' 

Workshop with the subsequent release of a draft version of the Haul Road Workgroup Final 

Report during the fall of 2011. 

Recycled/Recyclable • Printed wHh Vegetable OU Based Inks on 100".4 Recycled Paper (40% Post consumer) 
Attached to this letter is the Haul Road Workgroup Final Report that provides a "best 

practices guide" for modeling of haul road fugitive emissions in the AERMOD modeling system. 

This final report is being shared with the entire dispersion modeling community prior to the 1Oth 

Conference on Air Quality Models to promote broader consideration and facilitate further 

comment. Please send this report to your state, local and tribal agency modelers so that they can 

provide review and comment, as appropriate. The recommendations presented are not an 

endorsement by the USEP A as the definitive methodology for characterizing and addressing 

fugitive dust emissions from haul roads but should be considered a best practice approach based 

on the broad involvement of the co-regulating community in the development of this 

recommendation. 

We would like to give special recognition to the initiative and labors of Randy Robinson 

and Mick Daye in spearheading this initiative in 2009, chairing the Haul Road Workgroup, and 

developing this final report. We would also like to thank all of the federal, state, and local 

government dispersion modelers that participated in the Workgroup and assisted in the drafting 

of the final report presented in the attachment. 

Attachment: Robinson and Daye December 6, 2011 memorandum with Haul Roads 

Workgroup Final Report included as an attached document 
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGIONS 

77WESTJACKSONBOULEVARD 

CHICAGO, IL 60604-3590 

DEC. a 2011 '· REPlY TO THE ATTENTION OF' 

MEMORANDUM 

SUBJECT: 

FROM: 

TO: 

Haul Road Workgroup Final Report - 1 _. () I 

Randy Robinson, EPA Region~ -4~ Mick Daye, EPA Region 7 ~ ,t( ~ 

Tyler Fox, Leader, Air Quality Modeling Group 

George Bridgers, Clearinghouse Coordinator, Air Quality Modeling Group 

The purpose of this memorandum is to transmit the attached haul road modeling final 

report to the Air Quality Modeling Group. The report represents the collective efforts of the 

Haul Road Workgroup, which was formed following the 2009 Regional/State/Local Modeling 

Workshop. The purpose of the workgroup was to identifY and recommend a technically 

supportable approach for modeling haul road re-entrained dust. 

The attached document contains a summary of the possible options for modeling fugitive· 

road dust, a description of the sensitivity modeling conducted by the workgroup, and a tiered set 

of recommendations for modeling haul road fugitive emissions. The other attachment contains 

selected slides from the haul road presentation at the 2010 Regional/State/Local modeling 

workshop. The Workgroup requests Air Quality Modeling Group review and distribution of the 

recommendations document to the modeling community. 

Thank you and please contact us if you have any questions or require additional 

information. 

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1

Haul Road Workgroup Recommendations 

November 2011

Workgroup Charge -

The Haul Road Workgroup was formally established shortly after the May 2009 

Regional/State/Local Workshop. The purpose of the workgroup is to identify and 

recommend a technically supportable approach for modeling haul road re-entrained dust. 

While emission factors are a critical part of any roadway modeling exercise, this 

workgroup felt that emissions were outside our scope and did not engage in a review or 

evaluation of available fugitive dust emission factors. Based on modeling work and field 

study/journal article review, the following represents a recommendation for an approach 

to characterizing haul road fugitive emissions in AERMOD. 

Source Characterization - The model to be used for modeling haul road fugitive dust 

emissions is AERMOD. There are several ways haul road fugitive dust emissions can be 

characterized in AERMOD, including area source, volume source, and series of point 

sources. A line source algorithm is being developed but is not currently available. Each 

approach has advantages and disadvantages. The workgroup has considered each 

approach and a summary of the strengths and weaknesses is presented below. 

Area source advantages:

Can place receptors in ambient air contained within the area source

Easy to replicate dimensions of roadway in X and Y coordinates

Avoids the need to determine Sigma Y values (Sigma Z values are optional)

Can utilize a Sigma Z value if desired, to reflect an initial, well-mixed plume

Area sources explicitly simulate a uniform emission density across the roadway, 

which may be more realistic in some respects than other approaches. 

Area source disadvantages:

Area source in AERMOD does not have the meander algorithm 

Run times are generally longer than other approaches

Volume source advantages:

Volume source in AERMOD contains meander algorithm 

Conceptually, a volume source mimics an initial, well-mixed plume

Potentially faster run time than area source
2

Volume source disadvantages:

Concentrations are not calculated in a volume source exclusion zone 

o Exclusion zone is the region ( (2.15 x Sigma Y) + 1 meter)) from the 

center of the volume. 

Point Source with downwash advantages:

Precludes the need to establish Sigma values; handled internally by downwash

Conceptually, consistent with well-mixed plume

Can place receptors anywhere within roadway

Can be used for buildings near roadways

Point source with downwash disadvantages:

Downwash algorithm in AERMOD does not contain meander for receptors within 

the wake

Technique would be new to modeling community

Additional assumptions required, including building (truck) size, stack temp, 

velocity, height. 

Potential issues with BPIP used in this technique 

Sensitivity analysis 

Early in the process, the workgroup conducted an AERMOD sensitivity analysis to 

examine changes in haul road characterization inputs using volume and area source 

techniques. Limited, preliminary point source technique sensitivity runs were also 

conducted. Details of the sensitivity analyses are available at 

http://www.cleanairinfo.com/regionalstatelocalmodelingworkshop/archive/2010/Docume

nts/Presentations/RSL2010_HaulRoads.pdf . The following summarizes the setup and 

general conclusions. 

Analysis setup: 

 Used AERMOD Version 09292

 1 year of meteorological data (variety of locations)

 N-S and E-W crisscrossing road segments. Each 500m long, 10m wide.

 Flat Terrain

 Receptor Grids – Cartesian and Polar; beginning as near as possible to the volume 

sources. 1 meter from edge of area source. No receptors within source. 

 Unit emission rate 

 Evaluated range of values for top of plume height, Sigma Z, Sigma Y, and release 

height.

 Modeled using Adjacent Volume, Alternate Volume, and Area source 

representations.
3

 Calculated results for annual ave, peak 1-hr, 8th H 1-hr, peak 24-hr, 8th H 24-hr

 Point source modeling examined single vs multiple stacks and varying stack 

parameters. 

General Conclusions: 

 Increasing release height (and related Sigma Z) led to lower concentrations. 

 Increasing Sigma Y for alternate and adjacent volume sources lowered 

concentrations.

 For area source – increasing X dimension lowered concentrations at lower release 

heights (i.e., 0m and 0.5m). It had little impact at higher release heights (i.e, 1.5m 

and 3m). 

 For area source – adding a Sigma Z lowered concentrations for surface release 

heights, but generally increased concentrations at higher release heights

 For volume runs, adjacent gives higher concentrations than alternate. 

 Point Source – limited, preliminary modeling shows some sensitivity to stack 

height and velocity

 On-site meteorological data model runs showed same trends as with National 

Weather Service data, although concentrations were higher with on-site data. 

Model/Monitor Comparison

The workgroup was interested in locating field data to facilitate our review of haul road 

dispersion characteristics. Finding field data relevant to our task was difficult. While 

there are numerous field studies relevant to haul roads, the vast majority deal with 

monitoring designed to evaluate haul road emissions rather than dispersion 

characteristics. An evaluation conducted by OAQPS in 2006 examined haul road 

emissions from the Cordero Rojo Mine in Eastern Wyoming. The modeling looked at 

volume and area source configurations in AERMOD. The study, while limited, showed 

volume source characterizations performing slightly better than area source when 

compared to monitored PM10 data. The analysis was primarily designed to examine the 

impact of the meander algorithms. This is significant because the volume source 

approach incorporates meander while the area source approach does not. The difference 

in model performance was attributed to area source over-estimates due to lack of 

meander upwind dispersion. Details of the Cordero Rojo Mine evaluation results can be 

found at http://www.awma.org/events/confs/AQMODELS06/Session%204/4-

Roger%20Brode.pdf .
4

Haul Road Recommendations 

Definitions 

During the workgroup discussions and sensitivity modeling work, the following 

definitions were used; 

“VH” means vehicle height [~3m for typical haul trucks; ~10m for large mining trucks]

“VW” means vehicle width [~3m for typical haul trucks; ~10m for large mining trucks]

“VL” means vehicle length [~10m for typical haul trucks; ~20m for large mining trucks]

These definitions and associated dimensions were useful to the group as we discussed the 

various methods and developed the inputs to be used in the sensitivity modeling. They 

should not be treated as default values and/or used in place of site specific dimensions 

available for individual modeling demonstrations. 

General Recommendation

The following represents a general recommendation for modeling of haul road emissions. 

The recommendation is not meant to be prescriptive; local conditions and specific 

information may lead to an alternative approach. However, the workgroup feels that the 

recommendation presented below is reasonable, can be technically supported, and 

provides a level of conservativeness given the large amount of uncertainty associated 

with characterizing and simulating dispersion of fugitive emissions resulting from haul 

road traffic. Concentrations must be calculated in areas that are considered ambient air.1

Volume Source – Recommend for all haul roads, except for cases where 

ambient air receptors are within the volume’s exclusion zone (i.e., ( (2.15 x 

Sigma Y) + 1 meter)) from the center of the volume. 

Rationale: 

Volume source contains the meander algorithm.

Conceptually fits the physical parameters associated with well-mixed plume.

Limited model/monitor comparison study information supports volume source

Recommended Volume Source Configuration:

o Adjacent Volume Source 

 

1 Ambient Air is defined at 40 CFR Part 50.1(e) and further clarified in a December 19, 1980 from 

Douglas Costle to Senator Jennings Randolph. See http://www.epa.gov/scram001/guidance/mch/ama4.txt
5

o Top of Plume Height2– 1.7 x VH 

o Volume Source Release Height – 0.5 x Top of Plume height

o Width of Plume – VW + 6m for single lane roadways / Road Width + 6m 

for two lane roadways3. 

o Initial Sigma Z – Top of Plume / 2.15 AERMOD User’s Guide, Table 3-1

for use when modeling multiple volumes.

o Initial Sigma Y – Width of Plume / 2.15 AERMOD User’s Guide, Table 

3-1

o Emissions input as g/s

The 1.7 factor in the Top of Plume Height equation above is supported by 

information in a 2005 Atmospheric Environment paper by Gillies, et. al, entitled 

Effect of Vehicle Characteristics on Unpaved Road Dust Emissions. 

The Width of Plume value is based on a conservative adaptation of monitor 

placement guidance from EPA’s 1992 document, Guideline for Modeling Carbon 

Monoxide from Roadway Intersections. In that document, it is recommended that 

monitors not be placed nearer than 3 meters from the roadway edge to account for 

vehicle turbulence. Two-lane roadways are for cases with heavy two-way traffic 

where the combined plume needs to be approximated. Agencies may need to 

consider traffic counts, vehicle width, road width, and the amount of two-way traffic, 

in order to determine whether the roadway is best represented using single-lane or 

two-lane assumptions. While the workgroup’s sensitivity analysis indicates 

increased volume source width leads to decreased concentrations, our group didn’t 

specifically examine single-lane versus two-lane roadways. One option is to model 

two-lane roadways as two, single-lane volume sources. 

For cases where ambient air receptors fall within the volume source exclusion zone, a 

conservative volume source approach would be to reduce the width of plume 

dimensions enough so that the ambient air receptors are not inside the exclusion zone. 

Additionally, a mix of area sources and volume sources may adequately allow for 

consideration of all ambient air receptors. 

Area Source – Recommended for haul roads where ambient air receptors are 

located within source dimensions.

Rationale:

Volume source doesn’t allow placement of receptors within exclusion zone.

Area source can calculate concentrations at receptors within source. 

Area source can simulate volume source with use of similar release height and 

Sigma Z parameters.

 

2 Gillies, J.A., V. Etyemezian, H. Kuhns, D. Nikolic, D.A. Gillete, 2005. Effect of Vehicle Characteristics 

on Unpaved Road Dust Emissions. Atmospheric Environment, 39, 2341-2347

3 EPA. 1992. Guideline for Modeling Carbon Monoxide From Roadway Intersections. EPA-454/R-92-

005. http://www.epa.gov/scram001/guidance/guide/coguide.pdf
6

Recommended Area Source Configuration 

o Length – length of roadway segment (Aspect ratio in AERMOD extended 

to 100:1 before warning is issued. See Model Change Bulletin #3, 

Miscellaneous item #10) 

o Width – VW + 6m for single lane / Road Width + 6m for two-lane (same 

comment as for volume, two single-lanes is an option)

o Top of plume height – 1.7 x VH

o Release height – 0.5 x top of plume height 

o Sigma Z – Top of Plume height / 2.15

o Emissions input as g/s/m2

Point Source – The workgroup is not forwarding any point source recommendation 

at this time. There are potential benefits to this approach, however, more study is 

needed. 

Future Efforts

The workgroup understands that efforts are underway on a line source algorithm to be 

included in AERMOD. The time frame for completion of this work may be within the 

next couple years. A new line source algorithm would likely supplant the need to model 

haul road fugitive dust emissions using either volume, area, or point sources. 

Point source modeling of fugitive roadway emissions has some potential benefits, as 

noted earlier in this paper. One example is the ability to consider the influence of facility 

structures located near roadways when simulating the roadway fugitive dust in 

AERMOD. The Haul Road Workgroup supports further study of this approach. 

More field studies examining initial plume dimensions are encouraged. The effects of 

vehicle speed on the initial plume dimensions is an area that should be investigated when, 

or if, more field studies are conducted. 
7

References

Brode, R.W., Improved Algorithms for Modeling Impacts Near Roadways. MACTEC 

Federal Programs, Inc. A&WMA Specialty Conference, Denver, CO, April 2006

EPA. 1992. Guideline for Modeling Carbon Monoxide From Roadway Intersections. 

EPA-454/R-92-005. http://www.epa.gov/scram001/guidance/guide/coguide.pdf

EPA. 1994. Modeling Fugitive Dust Impacts from Surface Coal Mining Operations –

Phase II. EPA-454/R-94-025

Eskridge, R. E., Thompson, R.S., 1982, Experimental and Theoretical Study of the Wake 

of a Block-Shaped Vehicle in a Shear-Free Boundary Flow. Atmospheric Environment, 

16, 2821-2836

Fitz, D. R., 2001. Measurements of PM10 and PM2.5 Emission Factors from Paved 

Roads in California. Contract No. 98-723. California Air Resources Board, Monitoring 

and Laboratory Division

Gillies, J.A., V. Etyemezian, H. Kuhns, D. Nikolic, D.A. Gillete, 2005. Effect of Vehicle 

Characteristics on Unpaved Road Dust Emissions. Atmospheric Environment, 39, 2341-

2347.

Guideline on Air Quality Models, US Environmental Protection Agency, 40 CFR Part 51, 

Appendix W, November 9, 2005.

Heinerikson, A., Goodman, A., Anderson, K., Analysis of Haul road Emission Test Data 

for Determining Dispersion Modeling Parameters. Trinity Consultants. 

Reed, W. R., Performance Evaluation of a Dust-dispersion Model for Haul Trucks. 

National Institute for Occupational Safety and Health, Pittsburgh Research Lab. 

User’s Guide for the AMS/EPA Regulatory Model – AERMOD, US Environmental 

Protection Agency, EPA-454/B-03-001, September 2004.

Westbrook, J.A., Sullivan, P.S., Fugitive Dust Modeling with AERMOD for PM10

Emissions from a Municipal Waste Landfill. 

Williams, D.S., Manoj, K.S., Ross, J., Particulate Matter Emission by a Vehicle Running 

on Unpaved Road. 2008. Atmospheric Environment, 42, 3899-3905. 
1

Select Slides from May 2010 Regional/State/Local Workshop Presentation 

Sensitivity Analysis Work

 Used AERMOD Version 09292

 1 year of meteorological data (variety of 

locations)

 N-S and E-W crisscrossing road segments. 

Each 500m long, 10m wide.

 Flat Terrain

 Receptor Grids – Cartesian and Polar; 

beginning as near as possible to the volume 

sources. 1 meter from edge of area source. 

No receptors within source. 

Cont.

 Unit emission rate 

 Evaluated range of values for top of plume 

height, Sigma Z, Sigma Y, and release 

height.

 Modeled using Adjacent Volume, Alternate 

Volume, and Area source representations.

 Calculated results for annual ave, peak 1hr, 

8

th H 1hr, peak 24hr, 8th H 24hr, 
2

Matrix of Values for Analysis 

Range of Values

Top of Plume Ht 0m 1m 3m 5m 7m 10m

Sigma Z Top of Plume Height / 2.15

Sigma Y 3m / 2.15 10m / 2.15 16m / 2.15

Release Height Top of Plume Height / 2 
3

0

5000

10000

15000

20000

25000

Concentration ( g/m 3

)

0 0.5 1.5 2.5 3.5 5

Release Height (m)

Adjacent Volume Source - 1ST01H_Both

Changing Volume Width

Sigma Y = 1.4m

Sigma Y = 4.65m

Sigma Y = 7.44m

0

5000

10000

15000

20000

25000

Concentration ( g/m 3

)

1.4 4.65 7.44

Sigma Y (m)

Adjacent Volume Source - 1ST01H_Both

Changing Release Height

RH = 0m

RH = 0.5m

RH = 1.5m

RH = 2.5m

RH = 3.5m

RH = 5m
4

0

200

400

600

800

1000

1200

1400

1600

Concentration ( g/m 3

)

0 0.5 1.5 2.5 3.5 5

Release Height (m)

Adjacent Volume Source - ANNUAL_Both

Changing Volume Width

Sigma Y = 1.4m

Sigma Y = 4.65m

Sigma Y = 7.44m

0

200

400

600

800

1000

1200

1400

1600

Concentration ( g/m 3

)

1.4 4.65 7.44

Sigma Y (m)

Adjacent Volume Source - ANNUAL_Both

Changing Release Height

RH = 0m

RH = 0.5m

RH = 1.5m

RH = 2.5m

RH = 3.5m

RH = 5m
5
6

0

5000

10000

15000

20000

25000

30000

Concentration (g/m

3

)

0 0.5 1.5 3.5

Release Height (m)

Area Source - 1ST01H_BOTH

Road Dimension Change

X = 3m

X = 10m

X = 16m

0

5000

10000

15000

20000

25000

30000

Concentration (  g/m

3

)

3 10 16

X Dimension (m)

Area Source - 1ST01H_BOTH

Changing Release Height

No Sigma Z

RH = 0.0m

RH = 0.5m

RH = 1.5m

RH = 3.5m
7

MAX. CONCENTRATION - 89 ug/m3
8

Case Study

7m Top of Plume / 10m Plume Width

8th High 24-hour Ave.

0

200

400

600

800

1000

1200

1400

1600

1800

1

Scenarios Concentration (ug/m3)

Adjacent 

Alternate

Area - RH=0

Area - RH=3.5m

Area - RH=3.5/SZ=3.26

Adjacent vs Alternate

1-hr Average Results

0

5000

10000

15000

20000

25000

30000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Scenario Concentration (ug/m3)

Adjacent

Alternate
9
10
11

 POINT SOURCE WITH DOWNWASH
12