Shell Chukchi Sea Exploration Plan 

Revision 2

Environmental Impact Assessment

Attachment B

Air Quality Technical Report

Onshore Areas

Prepared for:

Bureau of Ocean Energy Management

Anchorage, Alaska

On behalf of:

Shell Gulf of Mexico Inc.

Anchorage, Alaska

Prepared by:

ENVIRON International Corporation

Lynnwood, WA

Date:

March 2015

Project Number:

2922291A
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Contents

Page

List of Tables................................................................................................................................................................3

List of Figures..............................................................................................................................................................3

Acronyms, Abbreviations, and Definitions................................................................................................................4

Preface .........................................................................................................................................................................7

1 Summary ...............................................................................................................................................................8

2 Project Description...............................................................................................................................................9

2.1 Exploration Program Activity Area.................................................................................................................9

2.2 Offshore Drilling Program Activities and Emissions Units ..........................................................................11

2.3 Onshore Exploration Program Activities and Emissions Units.....................................................................12

2.4 Spatial and Temporal Relationships of Offshore Drilling Program Emission Units.....................................12

3 Affected Environment........................................................................................................................................14

3.1 Ambient Air Quality Standards and Attainment Status.................................................................................14

3.2 Existing Air Quality Conditions....................................................................................................................16

3.3 Meteorological Conditions and Climate........................................................................................................18

4 Offshore Exploration Program Analytical Methods.......................................................................................21

4.1 Model Configuration of Emission Units .......................................................................................................21

4.2 Dispersion Modeling .....................................................................................................................................22

4.2.1 Dispersion Model Selection..............................................................................................................23

4.2.2 Methods............................................................................................................................................23

4.2.3 Domain .............................................................................................................................................23

4.2.4 Mesoscale Model Interface Format and Weather Research Forecast ...............................................24

4.2.5 Secondary Aerosols ..........................................................................................................................25

4.2.6 Downwash ........................................................................................................................................26

4.2.7 CALPUFF.........................................................................................................................................27

5 Drilling Program Modeling Results..................................................................................................................28

6 Onshore Activity.................................................................................................................................................30

6.1 Construction-Related Air Quality..................................................................................................................30

6.2 Onshore Facilities Analytical Methods.........................................................................................................30

7 Cumulative Exploration Program Concentrations .........................................................................................33

8 References ...........................................................................................................................................................34
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List of Tables

Table 1. Candidate Drilling Sites1

..........................................................................................................................9

Table 2. Applicable Ambient Air Quality Standards for Criteria Pollutants........................................................15

Table 3. Maximum Existing Ambient Air Concentrations...................................................................................16

Table 4. Maximum Predicted Concentrations Attributable to Offshore Sources (μg/m3)....................................28

Table 5. Construction Emissions (tons per year)..................................................................................................30

Table 6. Maximum Predicted Concentrations Attributable to Onshore Facilities (μg/m3) ..................................31

Table 7. Summary of Cumulative Modeled Onshore Emissions (μg/m3)............................................................34

List of Figures

Figure 1. Project Vicinity Map ..............................................................................................................................10

Figure 2. Regional Air Quality Monitoring Site Locations...................................................................................17

Figure 3. Wind Rose for Shell Burger Lease Area 2009-2010..............................................................................19

Figure 4. Wind Rose for Barrow, Alaska 2008 – 2012 .........................................................................................20

Figure 5. Orientation of Model Emissions Sources...............................................................................................22

Figure 6. Onshore Receptors Used in the CALPUFF Modeling ...........................................................................24

Figure 7. Locations of Maximum Onshore Concentrations...................................................................................29

Figure 8. Receptors Used In Onshore Facility Modeling Analysis .......................................................................32
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Acronyms, Abbreviations, and Definitions

Note that in this section and throughout the rest of this report there are active hyperlinks that will jump to 

the referenced material or section. General hyperlinks are formatted like this. Hyperlinks for tables and 

figures are highlighted like this.

Air quality standard................Health-based standard representing a pollutant concentration in the 

ambient air usually over some averaging period (e.g. 1-hour), intended 

to protect the health and welfare of people with a margin of safety.

Ambient air.............................the air in outdoor locations to which the public has ready access

Area source............................. an emission source type defined in CALPUFF. Area source emissions 

are released from two-dimensional four-sided areas

Attainment/Nonattainment ..... a determination and classification made by EPA indicating whether 

ambient air quality in an area complies with (i.e., attains) or fails to 

meet (i.e., nonattainment) the requirements of one or more NAAQS

Averaging time ....................... a specific period of time (e.g., 1 hour, 24-hours, 1 year) over which 

concentrations of an air pollutant are measured or model-calculated. 

Note that some NAAQSs are also based on multi-year averages of 

certain percentiles of measured or calculated concentrations.

BACT .....................................Best Available Control Technology

BOEM ....................................Bureau of Ocean Energy Management, the regulatory agency with air 

quality authority in portions of the Outer Continental Shelf, part of the 

Department of Interior.

CALPUFF ..............................Air quality dispersion modeling system used in this analysis. The 

CALPUFF modeling system consists of pre-processors, a dispersion 

model and post-processors. The meteorological preprocessor 

(CALMET) was not used to provide meteorological information. 

Instead meteorological data was provided by the Weather Research and 

Forecasting Model (WRF) and prepared for CALPUFF input using a 

specially designed program called the Mesoscale Model InterFace 

(MMIF).

CO .......................................... carbon monoxide, a criteria air pollutant

CO2 ......................................... carbon dioxide

CO2e .......................................Carbon dioxide equivalents (emissions of all GHGs expressed in terms 

of their "global warning potential")

Criteria air pollutant ............... an air pollutant specifically governed by the Federal Clean Air Act for 

which ambient air quality standards have been set. Criteria air 

pollutants include carbon monoxide, particulate matter, sulfur dioxide, 

nitrogen dioxide, ozone, and lead.

Dispersion model...................A computerized calculation tool used to estimate pollutant concentrations in the ambient air based on numeric simulations that consider the 

locations and rates of pollutant emissions and the effects of meteorological conditions, usually over specific averaging times (e.g., 8-hours)
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EPA ........................................US Environmental Protection Agency

hp............................................ horsepower

Meteorological data set........... a compilation of meteorological data representing conditions over 

some period of time and including such things as wind speed and wind 

direction, and formatted as required by the dispersion model being 

used. This analysis used a meteorological data set covering 5 years.

Micrometer/Micron ................ one millionth of a meter; typically used to distinguish particle size; 

typical human hair is 100 about microns in diameter

MLC .......................................Mud Line Cellar, an excavation below the level of the sea floor to 

protect drilling equipment from moving ice floes. 

MCL ROV System.................A remotely operated submersible excavation unit proposed for 

establishing MLCs.

MLC ROV System Vessel......A support vessel used to operate and support the MLC ROV System.

Modeling domain ...................the area included in the dispersion-modeling analysis

Modeling receptor .................. a theoretical (i.e., often non-specific) location used in computer 

modeling at which air pollutant concentrations are calculated. 

Modeling may also use site-specific receptors representing individual 

locations.

NAAQS ..................................National Ambient Air Quality Standard

NSPS ......................................New Source Performance Standard; rules that pertain to air pollution 

emission sources subject to air quality permits and newly manufactured 

equipment

NO2 ......................................... nitrogen dioxide, a criteria air pollutant

NOx ........................................ oxides of nitrogen, a general class of air pollutant without a specific air 

quality standard but used in monitoring air quality

Particulate matter (PM) .......... air pollutant comprised of solid or liquid particles; PM is usually 

characterized based on the particle size. See also PM10 and PM2.5.

PM10 ...................................... "Coarse" inhalable particulate matter with an aerodynamic size less 

than or equal to 10 micrometers (microns)

PM2.5 ..................................... "Fine" inhalable particulate matter with an aerodynamic size less than 

or equal to 2.5 micrometers (microns)

Point source ............................ an emission source type defined in AERMOD. Point source emissions 

are released from a single location.

ppm......................................... parts per million (a metric used in quantifying concentrations of air 

pollutants)

Receptor..................................See modeling receptor.

Release height......................... a CALPUFF term defining the height above ground at which source 

emissions are released

SO2..........................................Sulfur dioxide, a criteria air pollutant

tpy...........................................tons per year, an estimate of annual emissions
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μg/m3 .....................................micrograms per cubic meter (a metric used in quantifying 

concentrations of air pollutants)
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Preface

Shell Gulf of Mexico Inc. (Shell) has requested authorization from the United States Department of the 

Interior, Bureau of Ocean Energy Management (BOEM), to drill exploration wells in the Chukchi Sea 

beyond the 3-mile seaward boundary of Alaska. Exploration drilling will consist of the operation of two

drilling units with support vessels on the Outer Continental Shelf (OCS) of the Chukchi Sea. Shell 

already has an approved Exploration Plan (EP) for drilling in the Chukchi Sea at the Burger Prospect (EP 

Revision 1), but is making changes to that approved EP. 

This report was developed for Shell’s EP Revision 2 and its supporting Environmental Impact 

Assessment (EIA), for exploration drilling operations for Shell’s future seasons of operations. This Air 

Quality Technical Report presents the analytical methods and results of an analysis to estimate onshore 

air pollutant concentrations that may result from the drilling units, their support vessels, and onshore 

sources of air emissions associated with the exploration program.

BOEM implements its authority to protect air quality under 30 CFR Part 550 Subpart C. This program is 

referred to as the BOEM Air Quality Regulatory Program (AQRP). BOEM also has the responsibility to 

evaluate potential impacts of the exploration drilling program pursuant to the National Environmental 

Policy Act (NEPA). BOEM Alaska indicates that air quality modeling is required to evaluate potential 

impacts under NEPA.

1 This report details the methods, data, and predicted onshore concentration results 

of the NEPA air quality analysis. A separate report, provided in Attachment C of the EIA of EP Revision 

2, details the methods, data, and predicted offshore concentration results of the NEPA air quality analysis. 

1 Meeting between BOEM and Shell, May 15, 2013, held in BOEM office, Anchorage, Alaska
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1 Summary

This air quality analysis of the Shell OCS Exploration Program described in Shell’s EP Revision 2

identifies air pollutant emissions and onshore concentrations that may result from the air emissions from 

the exploration program. 

The air quality assessment of the exploration drilling program, as described in EP Revision 2, includes

development of detailed emission inventories based on spatially and temporally distributed emissions 

from the following emissions units:

Offshore Drilling Program

• Two drilling units, including

o Main generators

o Propulsion engines

o Small internal-combustion engines

o Seldom-used engines

o Heaters and boilers

o On-board incinerators

• Ice-management vessels (includes anchor handlers), including

o Propulsion and generator engines

o Boilers

o Incinerators

• Oil spill response vessels

• Offshore supply vessels

• Support tugs

• Oil storage tanker

• Science vessels

• MLC ROV System vessel

Onshore Program

• Onshore support activities, including

o Aircraft emissions

o A housing facility including associated generator engines 

o An airport hangar and storage building

o Miscellaneous onshore vehicles

Emissions from these units and activities were evaluated with air quality dispersion modeling. The air 

quality analysis considered emissions and concentrations of "criteria" air pollutants, including oxides of 

nitrogen, oxides of sulfur, particulate matter and carbon monoxide.
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2 Project Description

2.1 Exploration Program Activity Area

Shell proposes to continue the exploration drilling program in the Chukchi Sea, Alaska, that began in the 

2012 drilling season and is detailed in EP Revision 1. Shell’s proposed exploration drilling operations 

will take place on federal OCS leases in the vast Chukchi Sea, an area of approximately 230,000 square 

miles (mi2

). Shell’s EP Revision 2 proposes to conduct exploration drilling activities on six lease blocks 

all located within what is known as the Burger Prospect, acquired in federal OCS Lease Sale 193. The 

drill sites are remote from any infrastructure or human habitation and are located more than 60 miles 

offshore in Arctic waters that are inaccessible for eight months or more of the year due to pack ice. 

Shell’s seasonal exploration drilling operations would begin on or about July 1st and extend no later than 

October 31st. The sites are identified as “Burger” A, F, J, R, S and V in Table 1. The general location is 

depicted in Figure 1. 

Table 1. Candidate Drilling Sites1

Prospect Well Area Lease 

Number

Lease 

Block

Latitude Longitude UTM Coordinates3

X(m) Y(m)

Burger A2 Posey OCS-Y-2280 6764 N71° 18' 30.92" W163° 12' 43.17" 563945 7912759

Burger F Posey OCS-Y-2267 6714 N71° 20' 13.96" W163° 12' 21.75" 564063 7915957

Burger J Posey OCS-Y-2321 6912 N71° 10' 24.03" W163° 28' 18.52" 555036 7897424

Burger R Posey OCS-Y-2294 6812 N71° 16' 06.57" W163° 30' 39.44" 553366 7907999

Burger S Posey OCS-Y-2278 6762 N71° 19' 25.79" W163° 28' 40.84" 554391 7914199

Burger V Posey OCS-Y-2324 6915 N71° 10' 33.39" W163° 04' 21.23" 569401 7898125 1 Identified under Table 1.a-1 of Chukchi Sea EP Revision 2.

2 Burger A drill site where a partial well was begun in 2012.

3

 The Universal Transverse Mercator (UTM) coordinate system quoted here is from BOEM’s OCS Official Protraction Diagram and are based on the North 

American Datum 1983 (NAD-83), zone 3. The actual coordinates shown are the expected drill locations within each block.

Shell proposes to support the offshore drilling program with an onshore support facility located in the 

Barrow area. The facility is discussed in Section 6.
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Figure 1. Project Vicinity Map
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2.2 Offshore Drilling Program Activities and Emissions Units

The offshore drilling program will be conducted by two drilling units, the M/V Noble Discoverer

(Discoverer) and the Transocean Polar Pioneer (Polar Pioneer), with support from ice management 

vessels, anchor handlers, oil-spill response (OSR) vessels, offshore supply vessels (OSVs), tugs, tankers, 

science vessels, MLC ROV System vessel, and aerial transport. For the drilling units, the Discoverer and 

Polar Pioneer, the actual vessel to be used and the types of emission units on board are defined. Support 

vessels are contracted on a yearly basis and multiple vessels are able to meet the duty requirements for the 

needed tasks. As such, it is not certain that the support vessels currently considered for the exploration 

program will be available. Therefore, for the support vessels, a candidate vessel and the anticipated

emission units are identified.

The Discoverer is a turret-moored drilling unit that underwent significant upgrades in 2007 and 2013 so 

that it could operate in the Arctic. The Discoverer has its own propulsion engine for self-transport. The 

Discoverer is equipped with electrically powered thrusters, engine-driven electrical generators for the 

drilling motors, and other self-powered equipment such as hydraulic pumps, cranes, boilers, an 

incinerator, and other (mostly emergency-related) small sources. There will be no flares and no 

hydrocarbon-venting sources except for minor amounts associated with the drill cuttings. 

The Polar Pioneer is a semisubmersible vessel designed to operate in the arctic environment. The Polar 

Pioneer is transported by a towing vessel. The Polar Pioneer operates main generator engines, heaters 

and an incinerator. There will be no flares and no hydrocarbon-venting sources except for minor amounts 

associated with the drill cuttings.

The support vessels are equipped with diesel-fueled primary and emergency power generation engines, 

and in some cases incinerators and/or diesel-fueled boilers.

Ice management vessels and anchor handlers will assist with management of the drilling unit anchors, 

bow washing of any ice buildup on the drilling units, and some ice floe fragmenting in support of the ice 

management vessel. One anchor handler and one ice management vessel provide primary close support 

for each drilling unit with regard to these tasks. The ice management vessels are needed when there are 

ice features that require disruption in their path or fragmentation in order to provide protection for the 

drilling unit, or other assets critical to the safety of the exploration drilling program (i.e., mooring buoys, 

etc.). Up to two ice management vessels may be tasked to fragment any manageable ice flows so that the 

ice will flow around the drilling units. These ice management vessels may work at distances of 25 miles

or more upwind of the drilling unit to monitor the leading edge of any ice floe of possible concern. These 

activities are necessary for managing ice at distances that provide adequate response time for drilling 

units to get off a well and anchor in case of encroaching ice that cannot be managed. These response 

times may vary depending on the drilling stage of the well hole. Furthermore, the anchor handlers and ice 

management vessels may have other tasks to conduct beyond 25 miles of the drilling units. This 

operation is accounted for in the fuel consumption limits used to calculate emissions, but ENVIRON has 

assumed they will be within 25 miles for the entire season. As discussed below, this assumption is 

conservative and tends to over-predict onshore concentrations.

An oil-spill response vessel or vessels will be anchored nearby, typically between the two drilling units. 

During season, these vessels will primarily be used during refueling operations to protect against possible 

spills and will be located near the refueling Arctic oil fuel storage tanker. The OSR vessels are expected 

to be used in the unplanned and unlikely event of an oil discharge to the water. These vessels will be 

available to both the Discoverer and the Polar Pioneer.

Other support vessels include those for resupply and material transfer to shore. The OSVs would travel to 

the drilling units, then “park” in dynamic positioning (DP) mode beside the drilling unit for material or 
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personnel transfer. The OSVs may operate in DP mode beside the drilling unit and would remain there 

for approximately one day. 

It is anticipated that up to two science vessels similar to the OSVs will be primarily used to monitor 

discharges from each drilling unit as required by the National Pollutant Discharge Elimination System 

(NPDES) General Permit. These vessels may remain within a few miles of each drilling unit for these 

sampling periods or conduct secondary tasks, as needed. 

Two tugs will be operated in standby mode on-location in case the Polar Pioneer must leave location 

quickly because of encroaching ice. Another tug will escort the Discoverer to the drill site, assist during 

mooring, and depart during the season to conduct other activities outside the Chukchi Sea.

A fuel and oil tanker is expected to be located in an area between the two drilling units to resupply the 

drilling units and support vessels. 

During the 2012 drilling season, mud line cellars (MLC) were excavated with large drills aboard the 

Discoverer. As described in Shell's EP Revision 2, an MLC may also be excavated by a separate vessel 

(MLC ROV System Vessel) supporting a specially designed subsurface excavator. This MLC operation 

may proceed ahead of the Discoverer and Polar Pioneer to future well sites within the same lease blocks 

identified in Table 1.

If the ice management vessels or OSVs travel beyond 25 miles from the drilling units, air emissions 

would be dispersed to a greater extent than when the vessels are closer to the drilling units. Because the 

dispersion modeling conducted in this analysis concentrates all ice management and OSV emissions 

within 25 miles of the drilling units, it results in predictions that are higher than those expected if some 

vessels venture outside the 25 mile radius. Consequently, additional modeling of that scenario is not 

warranted.

2.3 Onshore Exploration Program Activities and Emissions Units

As discussed further in Section 6, there will be onshore support facilities, including housing for 

employees, hangars and other storage buildings, and transport of supplies and personnel. Onshore 

emission units related to the project could include power generation for personnel camps, material 

storage, helicopter hangers, transport vans and trucks, and helicopters in Barrow.

2.4 Spatial and Temporal Relationships of Offshore Drilling Program Emission Units

For air impact analysis purposes, there are three emission unit groups: the drilling units, the on-location 

support vessel support, and the onshore activities. Emissions units that are physically close together can 

have additive impacts, whereas, if the same emissions units are located over a large area, the impacts will 

be smaller at any one location (and distributed over a larger area). 

The emission units on the Discoverer and Polar Pioneer are concentrated on each drilling unit. The 

support vessels will be spread over a 25 mile radius of the Discoverer and Polar Pioneer; therefore,

emissions will be dispersed over this large area and will not be concentrated. At large distances from the 

drilling units, of up to 50 miles, the collective emissions will be well dispersed. 

The Discoverer and the Polar Pioneer will operate in separate lease blocks. Based on Table 1, the

distance between drill sites varies from 3 kilometers to 21 kilometers, depending on the two drill sites that 

are active at any given time. In order to evaluate the greatest potential onshore impact from the 

exploration activities, it is assumed that the drilling units are operating at the two lease blocks closest to 

shore, which are blocks J and V. This assumption will result in an analysis of the greatest potential 

onshore impacts because at distances larger than a few miles where there is no elevated terrain, air quality 
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concentrations are inversely proportional to the distance between the emission unit and the receptor. In 

this instance, the two drilling units are approximately 14 kilometers apart.

As discussed, the support vessels operate in different locations and operate in different ways over large 

areas. The anchor handler and ice management vessels will operate in areas determined by the drilling 

unit locations. When they are managing or scouting ice, they may typically be 25 miles or more upwind 

of the drilling unit. When these vessels are not working they could be anchored in warm-stack mode, 

transitioning or working in support of activities inside or outside of the OCS program area. 

The OSR vessels will normally be in an area between the Discoverer and the Polar Pioneer. These 

vessels will be in a stand-by mode or supporting refueling operations associated with exploration 

program.

Some emissions units may not operate concurrently. Only emissions units that operate concurrently can 

have additive short-term (1-hour and 24-hour) concentrations. Those that do not operate concurrently 

will not have additive short-term concentrations, although all will contribute to concentrations averaged 

over the season. Drilling and use of the drilling units’ smaller internal combustion (IC) engines will take 

place only after the drilling unit is fully anchored and connected to its anchors. The Discoverer’s 

propulsion engine will only be used intermittently once it is anchored. The cementing and logging 

equipment will only be used when setting casing or logging a well when the drilling unit is anchored at a 

drill site. None of the smaller diesels are operated during ship transit to and from the drill site. None of 

the smaller IC engines are used more than occasionally. However, since the precise times when 

individual emission units are expected to operate are not known at present, all units have been 

conservatively assumed to be operating concurrently in the air quality analysis.
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3 Affected Environment

3.1 Ambient Air Quality Standards and Attainment Status

Air quality is generally assessed in terms of whether concentrations of air pollutants are higher or lower 

than ambient air quality standards set to protect human health and welfare. Ambient air quality standards 

are established for what are referred to as "criteria" pollutants (e.g., carbon monoxide - CO, particulate 

matter, nitrogen dioxide - NO2, and sulfur dioxide - SO2). Onshore in Alaska, two agencies have 

jurisdiction over the ambient air quality accessible to the general public: the U.S. Environmental 

Protection Agency (EPA) and the Alaska Department of Environmental Conservation (ADEC). These 

agencies establish regulations that govern the concentrations of pollutants in the ambient air. Applicable 

state and federal ambient air quality standards are displayed in Table 2. These standards have been set at 

levels that EPA and ADEC have determined will protect human health with a margin of safety, including 

the health of sensitive individuals like asthmatics, the elderly, the chronically ill, and the very young.2

 

The ambient air quality standards are commonly used in NEPA assessments to evaluate onshore air 

quality impacts. 

Neither ADEC nor EPA maintain air quality monitoring stations on the North Slope of Alaska in the 

vicinity of the nearest onshore areas to the proposed exploration leases addressed here. In general, air 

quality monitoring stations are located where there may be air quality problems, and are usually in or near 

urban areas or close to specific large air pollution sources. Based on monitoring information for criteria 

air pollutants collected over a period of years, ADEC and EPA designate regions as being "attainment" or 

"nonattainment" areas for particular pollutants. Attainment status is therefore a measure of whether air 

quality in an area complies with the federal health-based ambient air quality standards for criteria 

pollutants. The North Slope of Alaska is classified as “attainment” or “unclassified” for all regulated air 

pollutants. In practical terms, “unclassified” areas are treated exactly the same as “attainment” areas. 

These designations are supported by monitoring data collected by private parties, such as Shell and BP. 

2 U.S. EPA, 2008a: Risk and Exposure Assessment to Support the Review of the NO2 Primary

National Ambient Air Quality Standard. EPA-452/R-08-008a, November 2008, Available at:

http://www.epa.gov/ttn/naaqs/standards/nox/data/20081121_NO2_REA_final.pdf

U.S. EPA., 2008b: Integrated Science Assessment for Oxides of Nitrogen -- Health Criteria.

EPA/600/R-08/071. July 2008. Available at:

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=194645

U.S. EPA, 2009: Risk and Exposure Assessment to Support the Review of the SO2 Primary

National Ambient Air Quality Standards: Final Report. EPA-452/R-09-007, July 2009, Available at:

http://www.epa.gov/ttn/naaqs/standards/so2/data/200908SO2REAFinalReport.pdf

U.S. EPA, 2010: Quantitative Health Risk Assessment for Particulate Matter. EPA-452/R-10-005, June 2010, Available at:

http://www.epa.gov/ttn/naaqs/standards/pm/data/PM_RA_FINAL_June_2010.pdf
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Table 2. Applicable Ambient Air Quality Standards for Criteria Pollutants

Pollutant Terms of Compliance (a) Concentration

Inhalable Particulate Matter (PM10)

24-Hour Average The 3 year average of the 98th percentile of the 

daily concentrations must not exceed

150 μg/m3

Fine Particulate Matter (PM2.5)

Annual Average 

24-Hour Average

The 3-year annual average of daily 

concentrations must not exceed

The 3-year average of the 98th percentile of 

daily concentrations must not exceed

12 μg/m3 (b)

35 μg/m3

Sulfur Dioxide (SO2) (b)

Annual Average 

24-Hour Average

3-Hour Average

1-Hour Average 

Annual arithmetic mean of 1-hour averages must 

not exceed

24-hour average must not exceed more than 

once per year

3-hour average must not exceed more than once 

per year

1-hour standard is attained when the three-year 

average of the annual, 99th percentile, daily 

maximum, one-hour concentration is less 

than or equal to

80 μg/m3

365 μg/m3

1,300 μg/m3

196 μg/m3

Carbon Monoxide (CO)

8-Hour Average 

1-Hour Average 

The 8-hour average must not exceed more than 

once per year

The 1-hour average must not exceed more than 

once per year

10,000 μg/m3

40,000 μg/m3

Ozone (O3)

8-Hour Average The 3-year average of the 4th highest daily 

maximum 8-hour average must not exceed

0.075 ppm

(150 μg/m3)

Nitrogen Dioxide (NO2)

Annual Average 

1-Hour Average 

The annual mean of 1-hour averages must not 

exceed

3-year avg. of 98th percentile of daily max 

1-hour averages must not exceed

0.053 ppm

(188 μg/m3

)

0.1 ppm

(100 μg/m3)

Lead (Pb)

Rolling 3-month Average Rolling 3-month average not to exceed 0.15 μg/m3

Note: μg/m3 = micrograms per cubic meter; ppm = parts per million

(a) All limits are federal and state air quality standards except as noted. All indicated limits represent "primary" air quality 

standards intended to protect human health.

(b) EPA issued a new 12 μg/m3 annual standard on 12/14/2012 that became effective on March 18, 2013; the previous annual 

standard was 15 μg/m3. The ADEC has yet to adopt the new standard.
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3.2 Existing Air Quality Conditions

There are no existing sources of air pollution near the Chukchi Sea lease area because it is more than 60 

miles from land and there are no other oil exploration or development sources in the Chukchi Sea at this 

time. In the absence of sources of emissions, the air quality in the project area is expected to be good. 

The points of land nearest the proposed drill sites are in the remote parts of the Arctic coast of Alaska, 

and are mostly uninhabited except for occasional subsistence hunting and fishing. The nearest native 

villages are at Wainwright and Point Lay, approximately 66 and 86 nautical miles away, respectively. 

Because the drill site location will be far from the Alaska shoreline and away from significant sources of 

pollution, existing air quality concentrations can be represented with a regional value. According to 

EPA’s Guideline on Air Quality Models (Guideline) (40 CFR 51, Appendix W, Section 8.2.2c), a 

“regional site” may be used to determine background concentrations if there are no monitors located in 

the vicinity of the source. A “regional site” is one that is located away from the area of interest, but is 

impacted by similar natural and distant man-made sources. The majority of the air quality data on the 

North Slope have been collected by various industrial developments associated with the oil and gas 

resources of the area. 

Shell and ConocoPhillips Alaska began monitoring NO2, PM2.5, PM10, SO2, CO, and O3 concentrations at 

Wainwright, Alaska in November 2008 and Point Lay, Alaska in June 2010. Both monitoring stations are

remotely located (minimal influence of industry and other human activities) and are representative 

“regional sites” on the North Slope for estimating offshore pollutant concentrations in the Chukchi Sea. 

However, both monitoring sites are located onshore and are located adjacent to villages and therefore may 

be exposed to high concentrations of pollutants from nearby combustion or unpaved road dust from 

vehicles. Consequently, it is expected that the measured concentrations of pollutants at these stations are

higher than the concentrations that actually occur offshore because the combustion and dust sources are 

not present on the open sea. A map of the ambient monitoring stations on the North Slope is provided in

Figure 2. 

Table 3 shows a summary of the background pollutant concentrations measured at the Wainwright and 

Point Lay monitoring stations during the drilling season (July 1 – Nov. 3). Comparison of the measured 

concentrations in Table 3 with the National Ambient Air Quality Standards indicates that existing 

concentrations are all well below ambient air quality standards for all pollutants and all averaging times. 

Table 3. Maximum Existing Ambient Air Concentrationsa

Pollutant Averaging 

Period

How standard is applied Wainwright 

Maximum

Measured

Concentration b

(μg/m3)

Pt. Lay 

Maximum 

Measured 

Concentration c

(μg/m3)

NAAQS 

(μg/m3)

NO2

1-hour 3-year average of 98th percentile 

daily maximum 1-hour averages 40.1 43.8 188

Annual Maximum arithmetic average 1.4 1.4 100

PM2.5

24-hour 3-year average of 98th percentile 

daily averages 10.7 5.5 35

Annual 3-year average of annual arithmetic 

averages

2.9 2.0 12

PM10 24-hour

Not to be exceeded more than once 

per year (2nd highs), averaged over 3 

years

73.0 23.6

150

SO2 1-hour 3-year average of 99th percentile 

daily maximum 1-hour averages 8.1 11.6 190
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3-hour Not to be exceeded more than once 

per year (2nd high) 12.8 14.1 1,300

24-hour Not to be exceeded more than once 

per year (2nd high) 2.2 13.4 365

Annual Maximum arithmetic average 0.4 4.8 80

CO

1-hour Not to be exceeded more than once 

per year (2nd high) 953 1490 40,000

8-hour Not to be exceeded more than once 

per year (2nd high) 946 1280 10,000

a Maximum background ambient air concentrations are calculated for the July 1st

- Nov. 30th “drill season” period, using the most recent available 

data from Wainwright and Pt. Lay monitoring stations. 

b Maximum concentrations measured at Wainwright from 2009 through 2012, as calculated according to the method described in “how standard 

is applied” column c Maximum concentrations measured at Pt. Lay monitoring site from 2011 through 2013, as calculated according to the method described in “how 

standard is applied” column. 

Figure 2. Regional Air Quality Monitoring Site Locations
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3.3 Meteorological Conditions and Climate

Climate in the project study area is unique to the polar region. The climate is dominated by severe cold 

temperatures during winter and a brief period of warming in late summer and early fall. 

From an air pollution perspective, the most important meteorological parameters are wind speed and 

direction because they determine the transport and dispersion of airborne contaminants. Wind conditions 

are commonly represented by a figure known as a wind rose. Figure 3 and Figure 4 depict wind roses

constructed from the meteorological data used in the offshore drilling program and onshore program air 

quality analyses, respectively. The figures have a series of bars emanating from the center of the drawing. 

The bars represent the relative frequency of wind directions with the length of each bar representing the 

relative frequency of the wind direction. Figure 3 and Figure 4 indicate the most frequent wind 

directions at the Burger Lease area and in Barrow are from the east-northeast. 

The colors in the figure illustrate the relative frequencies of wind speeds at the project site. The color 

code in the figure can be used to interpret the wind speeds.

Wind roses are indicative of dominant wind directions and thus also, the most frequent transport 

directions of air pollutants. Due to the higher transport frequencies, in many cases peak long-term 

average concentrations can be found downwind in these directions, because they occur more often and 

when averaged over a longer period of time can typically have higher average concentrations. This is not 

always the case, as other factors can contribute to the determination of peak downwind concentrations, 

such as the presence or absence of receptors in each downwind direction, terrain elevations in the 

downwind directions, wind speeds associated with each wind direction and air turbulence associated with 

each wind direction. Thus wind roses are useful when interpreting long-term average concentrations, 

with the above qualifiers. However, the wind rose gives little information on the peak short-term (e.g., 

hourly or daily) concentrations. As Table 1 shows, air quality is regulated on a variety of averaging 

times. Short-term impacts can occur in any wind direction, regardless of how common or frequent the 

wind direction is. As a result, in many air quality studies the peak short-term impacts are not at the same 

locations as the long-term concentrations, and are not necessarily aligned with the most common wind 

directions. 
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Figure 3. Wind Rose for Shell Burger Lease Area 2009-2010
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Figure 4. Wind Rose for Barrow, Alaska 2008 – 2012
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4 Offshore Exploration Program Analytical Methods

An air quality impact analysis includes two basic steps: (1) development of an emission inventory that 

identifies short-term and annual emissions related to the exploration drilling program, and (2) dispersion 

modeling to estimate resulting air contaminant concentrations in the ambient air. Appendix K of EP 

Revision 2 provides detailed documentation of projected emissions, including the basis for all 

calculations, attributable to the exploration activities described in EP Revision 2. Please refer to Appendix 

K of EP Revision 2 for further details. The following sections discuss the methods employed and the 

critical assumptions involved in the dispersion modeling analysis, which are based on the information 

provided in Appendix K of EP Revision 2.

A separate air quality modeling study was conducted for the onshore program located in the Barrow area. 

As discussed in Section 6, there are emissions associated with the onshore program but they represent 

only a small fraction of the total emissions. The emissions and setting associated with onshore program 

facilities (the Barrow personnel camp, the hangar and the helicopter usage) are very different from those 

associated with the offshore drilling program. Because the onshore facilities are located in Barrow, the 

emission units are much closer to the general population and therefore it is not appropriate to use the same 

methods of analysis for both offshore drilling activities and onshore activities. Accordingly, this section 

focuses mainly on the offshore drilling program emissions units (the Discoverer, the Polar Pioneer, and 

the support vessels), and the methods discussed in this section are those used in the evaluation of the 

offshore sources. Chapter 6 addresses the on-shore emissions units and modeling assessment. 

4.1 Model Configuration of Emission Units

All of the emission units associated with the exploration drilling program are to some extent mobile. The 

most stationary of the units are those on the drilling units. During the drilling of any individual well, the 

drilling unit remains fixed over the well. However, the Discoverer rotates about the drilling stem, placing 

the bow of the ship in the direction of the oncoming wind, which is usually also the direction any moving 

ice would come from. The Discoverer does not rotate as a result of the wind acting on it, but rather is 

moved by a cranking system aboard the Discoverer. As the vessel is rotated, the locations of many or all 

the emission units on the drilling unit are moved. The Polar Pioneer does not rotate with the wind.

Although the Discoverer emission units are mobile, for purposes of the modeling study, both drilling

units are assumed to be point sources at a fixed location. Given that the nearest onshore receptors are 

more than 100 kilometers from the Discoverer, the effect of the actual rotation of the ship is insignificant 

in the modeled concentrations. Hence the drilling unit is assumed to be pointing in the direction of the 

prevailing wind for the entire drill season. The prevailing wind direction was assumed to be coming from 

60 degrees measured clockwise from north based on buoy measurements taken at the Burger site during 

July to November 2009.

In contrast to the drilling units, the support vessel emissions units are much more mobile. Section 2.4 

describes the various types of movement and operation from each type of support vessel.

Given the highly mobile nature of these support vessels it is inappropriate to model them as fixed point 

sources, but rather as area sources where emissions are distributed over an area. For the ice management 

vessels, the area source is modeled as a large triangular area approximately 25 miles long and located 

upwind of the drilling unit. For the other vessels, a square area source, 2 kilometers on each side, is 

assumed to represent the remaining emission units. It is recognized that ice management vessels may be 

located further from the drilling units when managing ice, but the dimensions and locations used for these 

vessels have been selected to conservatively represent the spatial extent of their emissions.
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Figure 5 is a schematic drawing that shows the location of these point and area sources. Note that the 

large triangular areas are intended to represent the ice management vessel emissions. The four smaller 

square areas shown in the figure are used to represent the support vessels. One of these square areas is 

used to represent the MLC ROV System and its associated MLC ROV System vessel. The two areas 

shown directly downwind of the Discoverer and Polar Pioneer represent the close support vessels 

including the science vessel and any tugs dedicated to the drilling unit. The central area source, located 

between the two drilling units is the common fleet, including the Oil Spill Recovery vessels and the oil 

supply tanker. 

Figure 5. Orientation of Model Emissions Sources

4.2 Dispersion Modeling

ENVIRON International Corporation (ENVIRON) used air quality dispersion modeling simulations to 

estimate ambient concentrations attributable to emission units associated with the exploration program. 

This section discusses the methods used to develop these simulations.

Air quality models are computer programs designed to mathematically represent atmospheric transport 

and dispersion of airborne contaminants. The purpose of the proposed air quality modeling in this impact 

analysis is to provide estimates of ambient concentrations of air pollutants emitted by the various engines

boilers, and other emission units that are part of the exploratory drilling program described in EP 

Revision 2. 
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4.2.1 Dispersion Model Selection

The two air quality models most commonly recommended in the Guideline for industrial sources of 

emissions are the AERMOD model and the CALPUFF model. The AERMOD model is recommended by 

EPA for computation of concentrations within 50 kilometers of a source, while the CALPUFF model is 

recommended for locations farther than 50 kilometers from a source. Discussions with BOEM3 indicated 

the agency’s intention to follow EPA’s Guideline on Air Quality Models. While the Guideline provides 

no specific guidance on modeling offshore vessels, the guidance does suggest that when source-receptor 

distances are more than 50 kilometers, CALPUFF should be used.

ENVIRON applied CALPUFF to predict pollutant concentrations from emissions associated with Shell’s 

offshore drilling program in the Chukchi Sea. The CALPUFF predictions were used to display potential 

regional pollutant concentrations, assess compliance with the NAAQS on shore, and to predict 

concentrations at selected towns and villages or other locations of interest. The remainder of this section 

describes the long-range transport dispersion modeling techniques.

4.2.2 Methods

ENVIRON applied the regulatory version of the CALPUFF modeling system to simulate emissions from 

the offshore drilling program described in EP Revision 2. CALPUFF (Version 5.8) is the EPA 

recommended dispersion model for long-range transport analyses and source-to-receptor distances 

beyond 50 km.4

 For the application of CALPUFF, Shell followed the techniques recommended by the 

Federal Land Managers for Class I area assessments with a few modifications for Arctic conditions and 

available datasets. The simulations were performed based on a representative set of meteorological 

conditions from July to November 2007, 2008, and 2009, so as to best reflect drilling season conditions. 

EPA and ADEC practice is to accept meteorological data sets less than 10 years old for use with air 

dispersion modeling. Shell considers this data set to be representative because meteorology does not 

change dramatically on short time scales. The methods used to prepare the meteorological fields and 

perform the dispersion model analysis are described below.

4.2.3 Domain 

The area included in the dispersion-modeling analysis (i.e., the CALPUFF modeling domain) is shown in

Figure 6. The Burger site, several villages, and a 4-km receptor grid mesh size are posted on the domain

plot. The 4 kilometer grid size for receptors was selected in order to give coverage to the entire domain 

while still giving adequate resolution to concentrations. The analysis assumes the Discoverer and Polar 

Pioneer are located at the anticipated drill sites in Lease Blocks V and J, respectively. The CALPUFF 

domain is a rectangular 167-by-118 grid with a horizontal mesh size of 4 km and 10 vertical layers 

ranging geometrically from the surface to 4,000 m. A Polar Stereographic (PS) projection was used for 

the coordinate system with an origin at (70 N, 155 W) and standard latitude of 70 N. Receptors were also 

placed along the shoreline at a spacing of 1-km, at the villages, and places of interest shown on Figure 6, 

in keeping with BOEM recommendations at Shell’s meeting with BOEM on May 15, 2013.

3 Meeting between Shell and BOEM held on May 15, 2013 at BOEM’s offices in Anchorage Alaska.

4 40 CFR Part 51 Appendix W: Guideline on Air Quality Models
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Note: Receptor locations indicated in blue.

Figure 6. Onshore Receptors Used in the CALPUFF Modeling

4.2.4 Mesoscale Model Interface Format and Weather Research Forecast

The CALPUFF model requires meteorological data inputs to predict on-shore concentrations. This is 

achieved through the use of a meteorological data set and a preprocessor that prepares the information in 

a format that CALPUFF can accept. ENVIRON used the Weather Research Forecast (WRF) model to 

construct the meteorological fields and the Mesoscale Model Interface Format tool (MMIF)5 to process 

and reformat the WRF output for input to CALPUFF. EPA provided ENVIRON with WRF model 

simulations for the Chukchi Sea, which were then processed with MMIF (Version 2.3). These WRF 

simulations for July to November of 2007 to 2009 supported previous ConocoPhillips permitting 

activities in the Chukchi Sea.6

 The WRF simulations have the three domains with grid mesh sizes of 

5 Brashers, B., and C. Emery, 2013. Draft User’s Manual: The Mesoscale Model Interface Program (MMIF), Version 2.3, 2013-

4-30. Prepared by Environ International Corp. for U.S. EPA, OAQPS, Air Quality Assessment Division, Air Quality Modeling 

Group, Mail Code C439-01, Research Triangle Park, NC, 27771, Accessed at 

http://www.epa.gov/ttn/scram/dispersion_related.htm#mmif.

6 McNally, D. and Wilkinson, J.G., 2011. Model Application and Evaluation – ConocoPhillips Chukchi Sea WRF Modeling 

Application, Prepared by Alpine Geophysics, 7341 Poppy Way, Arvada, CO, 8007, November 21, 2011.
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36/12/4-km and 37 vertical levels. The boundary layer, nudging and other options selected for the WRF 

simulations are based on comparisons to Arctic meteorological data and the results of ongoing studies 

sponsored by BOEM.7

The WRF meteorological dataset for the Chukchi Sea has been evaluated against surface and upper air 

observations within the model 4-km domain including analyses focused on the coastal stations as a group, 

and at Wainwright and Barrow individually. The WRF simulations replicated observed temperatures, 

mixing ratios, wind speeds, wind directions, and precipitation totals within well-established model 

performance benchmarks.6 WRF also predicted the observed atmospheric structure aloft when compared 

to the observations at Barrow. The developers of dataset found the overall WRF model performance was 

better than previous datasets they evaluated for the intermountain west, Gulf Coast or eastern seaboard of 

the United States.6

ENVIRON used the following MMIF options, which are typical of most uses and follow model-guidance,

to process and reformat the WRF meteorological fields for CALPUFF:

• Use only the 4-km WRF inner domain;

• Select the GOLDER option for calculation of the Pasquill-Gifford stability class;

• Use layer mapping of the 37 vertical WRF levels to 10 layers with tops of 20, 40, 160, 320, 640, 

1200, 2000, 3000, and 4000m;

• No recalculation of the mixing height, the WRF diagnostic output will be used directly; and

• Trim five cells along from the outer edge of the WRF 4-km mesh size domain to account for 

potential edge effects in the WRF simulations.

ENVIRON used MMIF to prepare daily input files for CALPUFF to account for changing sea-ice 

coverage in the Arctic Ocean. The corresponding changes to the hourly energy fluxes and other 

important variables predicted by WRF governing dispersion and transport are already incorporated 

directly into the MMIF data provided to CALPUFF. However, several algorithms in CALPUFF (e.g. 

deposition velocity calculations) need to distinguish between over water and over land characteristics 

based on land use that is only provided at the start of each meteorological input file. Surface roughness 

changes from hour to hour over the water and seasonally over the land. Daily input files allow CALPUFF 

to consider more refined changes to land use for these algorithms. It should be noted that the surface 

roughness is calculated independently by WRF based on a two dimensional representation of the surface 

and is different for every grid cell in the surface domain. 

4.2.5 Secondary Aerosols 

CALPUFF incorporates algorithms to consider secondary aerosols formed by interaction and chemical 

transformations of emitted NOX and SO2. Total PM10 and PM2.5 were calculated from the sum of the 

emitted primary species, ammonium nitrate, and ammonium sulfate. The primary PM10 emissions for 

each source were divided into six species, including: soot or elemental carbon (EC), fine soil particles 

(PMF), coarse particles (PMC), organic carbon (OC), sulfate (SO4), and nitrate (NO3). PMC fractions 

were calculated from the difference between PM10 and PM2.5 emission rates. PM2.5 emissions were 

categorized into the remaining five species using the source profiles for diesel engines and incinerators 

7 Zhang, J., Liu, F., Krieger, J., Tao, W, and X. Zhang, 1981. Project Report for the 5-year Experimental Mesoscale Meteorology 

Reanalysis for the Beaufort/Chukchi Seas for Beaufort and Chukchi Mesoscale Meteorology Model Study. Prepared for US 

DOI, Bureau of Ocean Energy managements, Alaska Outer Continental Shelf Region, Anchorage Alaska, Contract 

0106CT39787, November 2011.
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based on profiles recommended by the EPA for the Community Multi-Scale Air Quality (CMAQ) 

model.8

 

Reaction rates and aerosol formation in the CALPUFF chemistry algorithms are influenced by 

background ozone and ammonia concentrations. ENVIRON used the maximum hourly ozone 

observations from the NOAA Barrow Observatory and BP’s Pad A monitoring site to represent 

background ozone concentrations in the simulations. The background ammonia concentration was 

assumed to be 0.5 ppb for all hours based on the Alaska Regional Haze Best Available Retrofit 

Technology (BART) modeling simulations.9

ENVIRON used the above quantitative methods to assess the contribution of emitted SO2 and NOx 

emissions to form secondary aerosols and assess PM2.5 concentrations. Although OCS activities in the 

arctic are not under EPA’s jurisdiction, EPA Guidance for PM2.5 Permit Modeling recommends an 

assessment of secondary aerosols when PM2.5 precursor emissions (NOx and/or SO2) emissions are 

greater than 40 tons per year.

10 EPA- recommended procedures include both quantitative and qualitative 

analyses. EPA’s Guidance provides a qualitative example based on a Region 10 Office assessment of 

Shell’s Discoverer drill ship and support fleet in the Chukchi Sea. EPA’s qualitative assessment:

“examined the regional background PM2.5 monitoring data and aspects of secondary PM2.5

formation from existing sources; the relative ratio of the combined modeled primary PM2.5

impacts and background PM2.5 concentrations to the level of the NAAQS; the spatial and 

temporal correlation of the primary and secondary PM2.5 impacts; meteorological characteristics 

of the region during periods of precursor pollutant emissions; the level of conservatism associated 

with the modeling of the primary PM2.5 component and other elements of conservatism built into 

the overall NAAQS compliance demonstration; aspects of the precursor pollutant emissions in the 

context of limitations of other chemical species necessary for the photochemical reactions to form 

secondary PM2.5; and an additional level of NAAQS protection through a post-construction

monitoring requirement.”

Region 10 found the formation of secondary aerosols would be limited in the Arctic and the NAAQS 

would be protected accounting for both the primary PM2.5 impacts and potential contributions due the 

PM2.5 precursors from the Discoverer and Associated Fleets.10 These same qualitative arguments apply to 

the exploration activities examined in this study.

4.2.6 Downwash

The tendency for exhaust plume rise to be reduced by wind flowing across nearby structures is referred to 

as downwash. Because the nearest receptors are located more than 100 km from the source at the 

shoreline, building downwash effects will not significantly affect the modeled results. However, previous 

modeling analyses for the Shell exploration program have developed building downwash parameters. 

The modeling did use the previous downwash values developed for the Shell exploration program in the 

8 CMAQ is the preferred regulatory model for PM2.5 and regional haze simulations. The EPA website containing PM speciation 

by source categories is: http://www.epa.gov/ttn/chief/emch/speciation/.

9 The Alaska BART and Regional Haze programs are described at http://www.dec.state.ak.us/air/anpms/rh/rhhome.htm. In the 

original BART simulations a background of 0.1 ppb was assumed. In the more refined simulations performed by applicants 

seeking exemption from BART, a more conservative 0.5 ppb ammonia concentrations was assumed.

10 EPA, 2014. Guidance for PM2.5 Permit Modeling. U.S. EPA, Office of Air Quality Planning and Standards, Air Quality 

Assessment Division, Research Triangle Park, NC, EPA-454/B-14-001, May 2014.
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CALPUFF modeling analysis for the Discoverer sources. New downwash parameters were created for 

the Polar Pioneer sources using EPA’s Building Profile Input Program (BPIP). 

4.2.7 CALPUFF 

ENVIRON performed six CALPUFF simulations using short-term and annual emissions for each July to 

November period of 2007 to 2009. Short-term and annual emissions are used in the analysis to address 

the different averaging periods of the NAAQS for each pollutant. The respective short-term and annual 

emission rates for emission units included in the simulations are presented in the emission inventory in 

Chapter 2.4 of Appendix K of EP Revision 2. It should be noted that drilling may occur between July 1 

and November 30 (153 days), but each drilling season is limited to 120 days. As the critical impacts are 

short term ambient standards and increments, not annual averages, Shell wanted to address concerns that 

drilling could occur at any time during the five month window. Therefore, in order to make certain the 

peak meteorological scenarios were evaluated, short-term emissions were conservatively modeled to 

occur during all 3,672 hours in the July 1 to November 30 drilling season for each of the three years in the 

simulations. 

It should be noted that CALPUFF addresses all pollutants in a combined single run. The interactions 

between pollutants, such as the secondary aerosol formation of particulate matter from gaseous oxides of 

nitrogen or sulfur are treated as chemical transformations in the model. These non-linear processes are 

modeled dynamically by CALPUFF for each hour and no aggregate or averaging methods are used.

The secondary aerosol is most commonly sulfates and nitrates, formed from sulfur dioxide and nitrogen 

oxides. To address secondary aerosol formation, ENVIRON applied POSTUTIL a program developed by 

the EPA, that converts particulate species such as sulfate and nitrate into the most common solid forms of 

these species, ammonium sulfate and ammonium nitrate, by converting mass to account for the difference 

in molecular weight between sulfate and ammonium sulfate, and nitrate and ammonium nitrate. It then 

sums all the particulate species to give total concentrations of PM10 and PM2.5. 

U.S. EPA regulatory default dispersion options used for long-range transport modeling were selected by 

invoking the MREG=1 switch within the input files. The CALPUFF utilities POSTUTIL and CALPOST 

were used to manipulate the large CALPUFF output files and summarize the results for comparison with 

the NAAQS. 

CALPOST (Version 6.221) was used to calculate the annual average and maximum concentrations for 

each averaging period and pollutant. Consistent with statistical format of the PM2.5 ambient standard, the 

8th highest daily PM2.5 concentration for each year of the simulations was calculated with CALPOST. For 

comparisons to the recent 1-hour NAAQS for SO2 and NO2, ENVIRON converted hourly time-series 

from CALPOST to files that mimic the output files from AERMOD. ENVIRON then applied a program 

to calculate the 8th highest daily 1-hour concentration and 4th highest daily 1-hour concentration, for NO2

and SO2, respectively, to match the statistical format of these ambient standards. 

ENVIRON conservatively assumed all NOX predicted at downwind receptors is NO2 for comparisons to 

the NAAQS. A second tier approach assuming a conversion factor of 0.8 is also appropriate and could be 

applied in any future analyses. It should be noted, although not performed here, a Tier 3 approach can be 

used to limit the potential formation of NO2 by the amount of ozone available. The Ozone Limiting 

Method (OLM) could be applied by post-processing the CALPUFF output files and assuming a constant 

NO2/NOX in-stack ratio, an equilibrium ratio of 0.8. The amount of NO2 formed will be limited using the 

same hourly ozone input file used in the CALPUFF simulations.
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5 Drilling Program Modeling Results

As depicted in Figure 6, 5,034 receptors were selected to evaluate onshore air quality. Maximum 

predicted concentrations from all 5,034 receptors are presented in Table 4 for each pollutant and 

averaging time. 

Table 4. Maximum Predicted Concentrations Attributable to Offshore Sources (μg/m3)

Pollutant Averaging 

Time

Modeled 

Concentration1

Background 

Concentration2

Total 

Concentration

NO2 1-hour 36 44 80

Annual 0.03 1.4 1

PM10 24-hour 4 24 28

Annual 0.02 NA 0.02

PM2.5 24-hour 4 5.5 10

Annual 0.02 2.0 2

CO 1-hour 12 1490 1502

8-hour 8 1280 1288

SO2 1-hour 0.1 11.6 12

3-hour 0.1 14.1 14

24-hour 0.03 13.4 13

Annual 0.0002 4.8 5 1 Averaged over a 20 square kilometer area

2 See Table 3.1.3-1 of the EIA in EP Revision 2. Point Lay selected as a representative site for background values for all 

categories except 1-hour and 3-hour SO2 (Wainwright selected for these categories).

The most representative maximum background air quality values available were selected for this 

evaluation. As depicted in Figure 7, maximum onshore concentrations determined by CALPUFF occur on 

the shoreline between Wainwright and Point Lay. The background concentrations from the nearest 

monitoring station to the modeled maximum concentration for each pollutant and averaging period were 

selected to estimate total concentrations reported in Table 4.1.1-1. Point Lay was the nearest monitoring 

station for all pollutants and averaging times except for peak 3-hour and 1-hour SO2 concentrations 

(Wainwright background values selected for these two categories). Although PM modeled peaks are 

nearer to Point Lay, Wainwright PM backgrounds were not considered representative because of 

contamination from road dust from the adjacent unpaved road discussed in SLR (2011) and SLR (2012).
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Figure 7. Locations of Maximum Onshore Concentrations
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6 Onshore Activity

The air quality issues for the onshore program facilities (the Barrow personnel camp, the hangar and the 

helicopter and aircraft usage) are very different from those associated with the offshore drilling program. 

The onshore program includes on-going operation of equipment associated with onshore program 

facilities. Additionally, as the onshore facilities are located in Barrow, the scale of potential air issues is 

much more local than for the drilling locations and the use of CALPUFF is not common for close 

distances. As discussed previously, the AERMOD model is recommended by EPA for computation of 

concentrations within 50 kilometers of a source, while the CALPUFF model is recommended for 

locations farther than 50 kilometers from a source. 

6.1 Onshore Facilities Analytical Methods

Shell proposes to support the offshore drilling program with an onshore support facility located in the 

Barrow area. The exact details of the facility are uncertain at this time, but some elements are known. 

From an air emissions and modeling perspective, the facilities include:

• A support personnel camp, housing 75 persons in Barrow;

• A kitchen, dining and recreation facility adjacent to the 75-person camp in Barrow;

• A hangar and warehouse at the Barrow airport with a boiler for heating; and

• Helicopter and fixed-wing aircraft operations at the Barrow airport for transport of personnel and 

some equipment to vessels at the Burger Prospect and for marine mammal surveys, and ice 

surveys.

Air Sciences, Inc. developed an estimated inventory of air quality emissions for the proposed onshore 

operations assuming maximum levels of activity and equipment. Details of these calculations can be 

found in Attachment B to Appendix K of EP Revision 2.

6.1.1 Dispersion Modeling

The air quality modeling for the onshore facilities was separated from the modeling of the offshore 

drilling program for two reasons:

• The distance between the drill sites and the onshore facilities is over 135 statute miles, so no 

significant overlap in the impact areas of the two operations is expected.

• The areas of potential impact for the onshore facilities are very close to those facilities, on the 

order of a mile or less, while the point of land nearest the drill sites is more than 60 miles away.

As a result of these two factors, the air quality modeling for the onshore facilities was performed 

separately, using a more appropriate air quality model, meteorological data, and receptors.

The onshore facilities were modeled with the EPA’s AERMOD model. AERMOD is recommended by 

EPA and other regulatory agencies as the appropriate model when the distance between the emission 

sources and the receptor is less than 50 kilometers. 11 Because the proposed onshore facilities are located 

near the Barrow airport, meteorological data from the Barrow Airport were the most appropriate for use 

in the modeling analysis. A five year data set covering the period from 2008 through 2012 was obtained 

11 40 CFR Part 51 Appendix W: Guideline on Air Quality Models
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for the Barrow Airport and processed through the AERMET meteorological pre-processor in preparation 

for running AERMOD. The Barrow airport collects both surface data and upper air data, and both data 

sets were used. Figure 4 is a wind rose depicting the Barrow airport data.

Because some of the activities take place at the Barrow airport, while others take place at the 75-person 

camp site to the north and east of Barrow, the modeling domain covered the entire Barrow area with the 

exception of two areas, one at the 75-person camp and one detailing the restricted area of the Barrow 

airport, that were eliminated from the grid because they are not considered ambient air due to restriction 

of access by the general public. A total 5,690 receptors were placed on a 100 meter-spaced grid covering 

the modeling domain. An additional 582 receptors were placed along the ambient air boundaries at a 

spacing of 10 meters. Figure 8 depicts the location of the receptors used in the onshore facility modeling 

analysis.

Emission units were modeled using a combination of point and area sources. The emissions from the 

camp area were modeled as three point sources reflecting the three generators that would be present at full 

build-out for the camp. A separate point source was used for the hangar/storage building, which could 

have a boiler for space heat. Finally, two area sources were used for the helicopter emissions and fixedwing aircraft emissions. 

The Emission and Dispersion Modeling system (EDMS) is a computer program commonly used for 

airports where aviation emissions are of interest. The EDMS has the capability to both calculate 

emissions and perform dispersion calculations of ambient concentrations. The EDMS model was used 

here only to calculate the emissions from the helicopter activity. EDMS also has the ability to implement 

the AERMOD model, entering runway and taxiway emissions as a series of area sources at different 

heights. Given the low level of emissions and simplicity of the Barrow Airport setting, AERMOD was 

applied directly with the emissions entered in two single area sources, one 702 meters long and 43 meters 

wide located at the center of the runway for the fixed-wing aircraft and a separate area source 119 meters 

long by 78 meters wide to represent the helicopter emissions near the hangers. EDMS was only used for 

calculation of emission rates. 

6.1.2 Onshore Program Modeling Results

The maximum predicted concentrations fall well below the NAAQS, as shown in Table 5. 

Table 5. Maximum Predicted Concentrations Attributable to Onshore Facilities (μg/m3)

Pollutant Averaging

Time

Modeled

Concentration

Background

Concentration1

Total

Concentration

NAAQS

NO2 1-hour 94 40.1 134 188

Annual 1 1.4 2.48 100

SO2 1-hour 19 8.1 27 196

3-hour 30 12.8 43 1300

24-hour 8 2.2 10 365

Annual 0.01 0.4 0.4 80

PM10 24-hour 6 23.6 30 150

Annual 0.03 NA NA NA

PM2.5 24-hour 6 5.5 11 35

Annual 0.03 2.0 2 12

CO 1-hour 1,198 953 2151 40,000

8-hour 326 946 1272 10,000 1 Wainwright selected as a representative site for background values for all categories except PM (Point Lay selected 

for PM). Wainwright particulate matter backgrounds were not considered representative because of contamination 

from road dust from the adjacent unpaved road discussed in SLR (2011) and SLR (2012).
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Note: Receptor locations indicated in blue. Sources of emissions indicated in green.

Figure 8. Receptors Used In Onshore Facility Modeling Analysis
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7 Cumulative Exploration Program Concentrations

Although no significant overlap is expected between concentrations of air pollutants resulting from the 

off-shore drilling emission sources and those from the on-shore sources due to the large separation 

distance, a brief examination of potential cumulative concentrations is provided. This analysis is 

provided as a conservative over-statement of potential peak concentrations because it assumes 

meteorological conditions would occur simultaneously that produced the peak concentrations from the 

off-shore drilling program and the on-shore emission units, which does not occur in the meteorological 

data set. The current analysis is provided only because overlapping impacts, even computed by these 

unrealistic assumptions, are still below criteria, and thus provides a screening analysis, and eliminates the 

need for a more comprehensive analysis of cumulative impacts.

Concentrations at receptors in Barrow computed by the CALPUFF model for the drilling units and 

support vessels emission units were examined to determine the potential for overlapping concentrations. 

These would generally not be additive with the onshore facility concentrations for the short-term 

averaging times (1-hour, 3-hour, 8-hour and 24-hour), because the meteorological conditions that produce 

peak concentrations from the off-shore emissions units are not the same as the conditions that produced 

peak concentrations from off-shore emission units. Highest concentrations from the off-shore sources in 

Barrow for 1-hour NOX were predicted to be 8 μg/m3

. Highest 1-hour CO concentrations are at most 3 

μg/m3 from off-shore sources. All other pollutants and averaging times show off-shore source impacts in 

Barrow of less than 2 μg/m3

. 

Adding these concentrations to those predicted for the on-shore sources would not result in totals that 

exceed the NAAQS. Table 6 includes a summary of the impacts modeled onshore from sources of 

emissions offshore and onshore. The total concentrations do not necessarily indicate that dispersion 

modeling for a particular receptor location provided results that were additive. As stated, overlap of 

short-term concentrations is not expected to occur due to the large separation distances and prevailing

meteorological conditions. 

Table 6 Summary of Cumulative Modeled Emissions Onshore (μg/m3)

Pollutant Averaging

Time

Modeled 

Concentration 

from Offshore 

Sources

Modeled

Concentration

from Onshore 

Sources

Background

Concentration

Total

Concentration 1

NAAQS

NO2 1-hour 8 94 40.1 142 188

Annual 0.008 1 1.4 2 100

SO2 1-hour 0.03 19 8.1 27 196

3-hour 0.02 30 12.8 43 1300

24-hour 0.006 8 2.2 10 365

Annual 0.00004 0.01 0.4 0.4 80

PM10 24-hour 1.40 6 23.6 31 150

Annual 0.008 0.03 NA NA NA

PM2.5 24-hour 1.40 6 5.5 13 35

Annual 0.008 0.03 2.0 2 12

CO 1-hour 3.3 1,198 953 2154 40,000

8-hour 1.9 326 946 1274 10,000

1 Offshore concentrations are not expected to be additive with the onshore facility concentrations for the short-term averaging times (1-hour,3-

hour, 8-hour and 24-hour), because the meteorological conditions that produce peak concentrations from the off-shore emissions units are not 

likely to be the same as the conditions that produced peak concentrations from off-shore emission units.
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8 References

US Environmental Protection Agency (EPA)

2004. AERMOD User's Guide. EPA-454/B-03-001. September 2004

CALPUFF User’s Guide