MEMORANDUM 

SUBJECT: Fenceline Ambient Benzene Concentrations surrounding Petroleum Refineries 

FROM: Ted Palma, Physical Scientist 

 USEPA/OAQPS/Health and Environmental Impacts Division 

 Darcie Smith, Physical Scientist 

 USEPA/OAQPS/Health and Environmental Impacts Division 

TO: Brenda Shine, Environmental Engineer 

 USEPA/OAQPS/Sector Policies and Programs Division 

DATE: January 7, 2014 

Background 

Benzene is a key hazardous air pollutant emitted by all petroleum refineries. To support the effort to 

develop a fenceline monitoring program around petroleum refineries, EPA risk assessors estimated the 

maximum chronic off-site ambient benzene concentrations surrounding each of the 148 petroleum 

refinery facilities in the country based on the benzene emissions inventory developed for these sources. 

Approach 

In support of the residual risk and technology review required by CAA sections 112(f) and 112(d)(6) 

for this source sector, on April 1, 2011 EPA sent out an information collection request (ICR) under the 

authority of Section 114 of the CAA to the petroleum refining industry. The ICR requested available 

information regarding process equipment, control devices, point and fugitive emissions of all HAP, 

practices used to control fugitive emissions, and other aspects of facility operations, including stack 

parameters and locations for each of the two refinery source categories (MACT 1 and MACT 2) covered 

in the proposed rulemaking as well as all other sources present at the facility (i.e., whole facility). 

Details on the ICR and development of the emissions inventory for risk assessment modeling can be 

found in the National Emission Standards for Air Pollutant Emissions: Petroleum Refinery Sector. This 

is believed to be the best available, most current emissions inventory for this industry. Further, EPA 

used this inventory to develop estimates of HAP emissions at each facility after full implementation of 

the proposed standards, calling this the “post-control” emissions inventory. While the ICR and 

emissions inventories contained estimates of all hazardous air pollutants emitted from the facility, as 

noted above benzene was selected as a surrogate for purposes of estimating fenceline HAP 

concentrations. Following development of the post-control emissions inventory, long- term ambient 

concentrations for each facility in the source category were estimated using the EPA’s American 

Meteorological Society/EPA Regulatory Model dispersion modeling system (AERMOD). The 
AERMOD is a state-of-the-science Gaussian plume dispersion model that is preferred by EPA for 

modeling point, area, and volume sources of continuous air emissions from facility applications. The 

model is used to develop annual average ambient concentrations through the simulation of hour-by-hour 

dispersion from the emission sources into the surrounding atmosphere. Hourly emission rates used for 

this simulation are generated by evenly dividing the total annual emission rate from the inventory into 

the 8,760 hours of the year. Concentrations are estimated by the model at a set of polar grid receptors 

centered on the facility as well as surrounding census block centroid receptors extending from the 

facility outward to 50 km. For purposes of this modeling analysis, EPA assumed that the nearest offsite polar grid receptor (P) was the best representation of each facility’s fenceline concentration in the 

post-control case, unless there was a census block centroid that was nearer to the fenceline than the 

nearest off-site polar grid receptor. In those instances, EPA estimates the fenceline concentration as the 

concentration at the census block centroid (C) (see Attachment 1). Only receptors (either the polar or 

census block) that were estimated to be outside the facility fenceline were considered in determining the 

maximum benzene level for each facility. Meteorology for the analysis generally consisted of a single 

year of data from a nearby national weather service office. Further details on the approach used are 

provided in the source category risk assessment report (Draft Residual Risk Assessment for the 

Petroleum Refining Source Sector USEPA, January 2014). 

Results 

Individual facility estimates of the maximum ambient annual average offsite benzene concentration are 

provided in Attachment 1. The maximum offsite annual average at any facility is estimated to be 9 

μg/m3

. The average of the estimated maximum concentrations across all 142 facilities is 0.8 μg/m3. 

Four facilities are estimated to create ambient benzene levels at or above 4 μg/m3, while 36 are 

estimated to create maximum ambient benzene levels above 1 μg/m3. In most cases, maximum off-site 

annual average concentrations are estimated to occur at or just adjacent to the facilities fenceline. Figure 

1 shows the value and location of the maximum facility-level annual average benzene concentration at 

the facility with the highest modeled value in this analysis. As the figure illustrates, this concentration is 

near, but just outside of, the fenceline of the facility. 

It is important to keep in mind that these estimates of ambient benzene concentrations are due only to 

the facility-specific emissions of benzene in the inventory noted above and do not reflect ambient levels 

from other nearby sources of benzene such as adjacent facilities or mobile source emissions. Further 

the estimates do not include potential contributions from unidentified or unquantified on-site sources, 

and are subject to the typical uncertainties associated with estimating emissions and modeling 

atmospheric dispersion. We note that a recent model-to-monitor comparison of chronic ambient 

benzene concentrations conducted for the 2005 National Air Toxic Assessment (NATA) 

(http://www.epa.gov/ttn/atw/nata2005/05pdf/nata2005_model2monitor.pdf), which utilized the same 

modeling approach, found average model-to-monitor ratios between 0.9 to 1.1. Thus, we have a high 

degree of confidence that the dispersion modeling approach utilized in this analysis will provide 

accurate benzene concentrations adjacent to the subject facilities. 

 
Figure 1. Maximum Off-site Annual Average Benzene Concentration Adjacent to Facility NEI33031 

Attachment 

cc: Erika Sasser 

 Kelly Rimer 
Facility NEI ID Max Conc (ug/m3)

Census Block /

Polar Receptor Latitude Longitude

NEI33031 9                                       P 29.99787 ‐90.39704

NEI12988                                      5 P 36.66466 ‐97.08543

NEI12711                                      4 P 29.72632 ‐95.25439

NEI33010                                      4 P 30.13709 ‐93.32137

NEI12486                                      3 P 28.46254 ‐98.18753

NEI876 3                                       P 33.20236 ‐92.67681

NEI12458 3                                       P 45.65532 ‐108.76732

NEI6166 3                                       P 30.19286 ‐93.32202

NEI18372 3                                       P 30.77933 ‐88.05951

NEI42016 3                                       P 40.84067 ‐111.92355

NEI11663 2                                       P 40.71274 ‐84.12492

NEI6130 2                                       C 30.47764 ‐91.20601

NEI42583 2                                       P 46.69099 ‐92.06588

NEI32762                                      2 P 37.79026 ‐96.87261

NEI371                                      2 P 42.86427 ‐106.23821

NEI40732                                      2 C 41.83017 ‐79.12470

NEI6136                                      2 C 30.53457 ‐91.75137

NEI41864                                      2 P 27.84163 ‐97.52475

NEI55835                                      2 P 38.84236 ‐90.05380

NEI40723                                      2 C 39.92161 ‐75.19419

NEI34898                                      2 P 32.85445 ‐104.39475

NEI6519                                      1 P 29.06465 ‐95.75525

NEI49781                                      1 C 39.00496 ‐87.72556

NEI2KS125003                                      1 P 37.05288 ‐95.60760

NEI11715                                      1 P 41.68487 ‐87.47388

NEI34907                                      1 P 35.48633 ‐108.42925

NEI42020                                      1 C 40.89069 ‐111.91001

NEI11449                                      1 C 41.69193 ‐83.44726

NEI34050                                      1 P 44.85609 ‐93.00545

NEI42370                                      1 P 47.25273 ‐122.39775

NEI46556                                      1 C 17.71525 ‐64.75793

NEI12460                                      1 P 45.82142 ‐108.42977

NEI11192                                      1 C 31.76743 ‐106.40501

NEI7130                                      1 P 29.34569 ‐98.46071

NEI18406                                      1 C 64.72880 ‐147.35141

NEI11574 1                                       P 40.77267 ‐81.42201

NEI18408 0.9                                   P 64.73552 ‐147.34841

NEI13322 0.9                                   P 21.30509 ‐158.11450

NEI42382                                  0.9 C 48.46419 ‐122.56796

NEI11885                                  0.8 C 42.27993 ‐83.14936

NEI12084                                  0.8 P 27.82325 ‐97.48873

NEI34057                                  0.8 P 30.32060 ‐88.48512

Attachment 1

Maximum Predicited Off‐Site Ambient Benzene Concentrations

1 of 4
Facility NEI ID Max Conc (ug/m3)

Census Block /

Polar Receptor Latitude Longitude

NEI6062                                  0.8 C 30.25247 ‐93.27236

NEI6436                                  0.7 C 29.38094 ‐94.92845

NEI20616 0.7                                   P 33.87289 ‐118.15978

NEI363                                  0.7 P 41.12698 ‐104.78535

NEI53718                                  0.7 P 41.42458 ‐88.18414

NEI6022                                  0.7 P 30.47572 ‐91.19501

NEI6123                                  0.6 C 29.94009 ‐89.97174

NEI02185REF5                                  0.6 P 70.32646 ‐149.60504

NEI109                                  0.6 C 39.81992 ‐75.41974

NEI6127                                  0.6 C 29.93644 ‐89.94282

NEI7781 0.6                                   C 29.73146 ‐95.01372

NEIWYT$12156                                  0.5 P 41.26311 ‐110.80647

NEI05139REF11                                  0.5 P 33.36493 ‐92.71275

NEI42413                                  0.5 P 48.89636 ‐122.74343

NEI46752                                  0.5 P 40.61551 ‐80.63267

NEI43243                                  0.5 C 41.77862 ‐107.11276

NEI7233                                  0.5 P 30.07883 ‐94.07318

NEI33008                                  0.5 C 32.47127 ‐93.79299

NEI02185REF4                                  0.5 P 70.25488 ‐148.35501

NEI11119                                  0.4 P 29.73121 ‐95.11721

NEI40371                                  0.4 P 46.85179 ‐100.87070

NEI12969                                  0.4 P 36.14521 ‐96.00874

NEI11450                                  0.4 C 41.63321 ‐83.49532

NEI26473                                  0.4 P 32.10499 ‐81.12462

NEI41591                                  0.4 P 35.08812 ‐90.07445

NEI6475                                  0.4 C 32.36581 ‐95.28325

NEI11200                                  0.4 P 29.87087 ‐93.96614

NEINJT$891                                  0.4 C 39.84275 ‐75.24790

NEI12044                                  0.4 C 29.37901 ‐94.91078

NEI7988                                  0.4 P 27.80914 ‐97.43264

NEI34061                                  0.4 P 31.81567 ‐89.00746

NEI2NV110905                                  0.3 P 38.62078 ‐115.61904

NEI20154                                  0.3 P 35.39483 ‐119.04533

NEI26533                                  0.3 P 21.30106 ‐158.09667

NEI6116                                  0.3 P 29.66963 ‐89.97074

NEI6963                                  0.3 P 35.70064 ‐101.35233

NEI12791 0.3                                   P 29.37451 ‐94.88921

NEI7441 0.3                                   P 29.90022 ‐93.97262

NEI42040 0.3                                   C 40.79986 ‐111.91444

NEI41863                                  0.3 C 27.80795 ‐97.45492

NEI12480                                  0.3 P 29.73071 ‐95.21391

NEI40531                                  0.3 P 34.63584 ‐97.16458

NEI21130                                  0.3 P 33.89713 ‐118.14268

NEI32864                                  0.3 C 38.37415 ‐82.58674

NEI41771                                  0.3 P 29.95579 ‐93.89364

2 of 4
Facility NEI ID Max Conc (ug/m3)

Census Block /

Polar Receptor Latitude Longitude

NEI42081                                  0.3 P 40.83179 ‐111.92444

NEI19870                                  0.3 P 38.05765 ‐122.26078

NEI12459                                  0.3 P 45.78384 ‐108.48222

NEI42425 0.3                                   P 48.83963 ‐122.69135

NEI42381 0.3                                   C 48.48863 ‐122.55232

NEI13371 0.2                                   C 60.67983 ‐151.36597

NEI32801                                  0.2 C 38.36035 ‐97.67430

NEI6617                                  0.2 P 27.81467 ‐97.49765

NEI40039REF1033                                  0.2 P 35.69350 ‐98.66335

NEI42309 0.2                                   P 37.22601 ‐76.43341

NEI404 0.2                                   P 43.84852 ‐104.21797

NEI25450                                  0.2 P 38.06709 ‐122.12377

NEI7134                                  0.2 P 27.81565 ‐97.41899

NEI12968                                  0.2 P 36.11221 ‐96.00698

NEI6375                                  0.2 C 40.64209 ‐74.22462

NEI12464                                  0.2 P 47.52463 ‐111.28821

NEI19587                                  0.1 P 37.94334 ‐122.38152

NEI6084 0.1                                   C 30.10181 ‐90.90758

NEI34022                                  0.1 P 44.75330 ‐93.03728

NEI20467                                  0.1 C 33.91713 ‐118.40801

NEI889                                  0.1 P 39.80721 ‐104.94512

NEI113 0.1                                   C 39.82745 ‐75.39881

NEINMT$12478                                  0.1 P 32.87441 ‐103.29923

NEI6087                                  0.1 C 30.05835 ‐90.59093

NEI20966                                  0.1 P 33.94597 ‐118.16408

NEI2CA254640                                  0.1 P 34.93051 ‐120.51069

NEI46764                                  0.1 C 41.97837 ‐78.62008

NEI18394                                  0.1 P 33.19440 ‐87.60883

NEI2CA314628 0.1                                   P 38.03532 ‐122.06583

NEI11232 0.1                                   C 29.73114 ‐95.23785

NEIOKT$11009                                  0.1 P 34.21512 ‐97.10752

NEI53702                                  0.1 C 41.64506 ‐88.04593

NEI32353                                  0.1 P 37.93962 ‐87.91624

NEI20103                                  0.1 C 35.29259 ‐118.91221

NEICA0370363                                  0.1 P 33.77005 ‐118.27736

NEI2CA131003                                  0.1 C 33.79987 ‐118.22104

NEI19834                                  0.1 P 38.03548 ‐122.12911

NEICA0379991                                  0.1 P 33.80050 ‐118.23818

NEI20797                                0.05 P 33.79579 ‐118.23827

NEICA1910268                                0.04 C 33.79232 ‐118.22299

NEI6095                                0.04 P 30.00204 ‐90.39014

NEI21034                                0.04 P 33.85210 ‐118.31716

NEI34872                                0.04 P 40.56527 ‐74.25004

NEI6446                                0.03 P 32.27176 ‐101.42189

NEI32997                                0.02 P 37.07069 ‐84.61031

3 of 4
Facility NEI ID Max Conc (ug/m3)

Census Block /

Polar Receptor Latitude Longitude

NEI8139                                0.02 C 35.94462 ‐101.90042

NEI19869                                0.02 P 35.03892 ‐120.59734

NEI21466                                0.01 C 33.77764 ‐118.24223

NEI01053REF1_5 0.01                                 P 31.18032 ‐87.43803

NEI26218 0.01                                 C 39.57491 ‐75.60037

NEI20174 0.01                                 P 35.36919 ‐119.08154

NEI33007                                0.01 P 32.59303 ‐93.51312

NEI34873                              0.003 C 40.53223 ‐74.26406

NEI34069                              0.002 P 32.41064 ‐90.91859

NEI18415 0.001                               P 61.06517 ‐146.29024

4 of 4