Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-1 

6 Air Quality Impact Assessment 

On July 23, 2012, ENVIRON International Corporation (ENVIRON) submitted to EPA Region IV 

and the U.S. Fish and Wildlife Service (FWS) an Air Quality Analysis Modeling Protocol for the 

StatOil Gulf Services, LLC (Statoil) OCS Permitting Project (OCS Project). ENVIRON 

responded to EPA and FWS comments on the protocol (telephone conversation with EPA’s 

Stan Krivo on August 23, 2012; and via email from FWS on July 30, 2012). ENVIRON followed 

the protocol, with the FLM/EPA requested changes/additions, in performing this air quality 

impact assessment. The original PSD application was received by EPA on September 10, 2012 

As documented in Section 4.1 of the original PSD permit application, the pollutants subject to 

Prevention of Significant Deterioration (PSD) review for the proposed Statoil exploration 

activities are NOX and PM2.5. Direct PM2.5 emissions did not trigger PSD review, but emissions 

of a PM2.5 precursor (NOX) is subject to PSD review. 

The original PSD application was deemed incomplete on October 10, 2012. ENVIRON 

responded with additional information requested by EPA on December 10, 2012; January 30, 

2013; and April 25, 2013. An updated version of this assessment (a revised Section 6 of the 

original application) was included in the January 30, 2013 submittal. In that version of this 

assessment, ENVIRON used a series of volume sources to represent the support vessels and 

crew boats emissions as they arrived at and departed from the drilling vessels, in a run 

designed to assess short-term Class II SILs. Subsequently, EPA’s Mr. Stan Krivo requested a 

more conservative modeling approach for these support vessels and crew boats. 

This version of the air quality impact assessment includes a revised treatment of the support 

vessels and crew boats for the short-term modeling, using point sources. A copy of the updated 

CALPUFF modeling files for the Developer and Discoverer Americas will be sent on DVD under 

separate cover. 

On January 22, 2013, the PM2.5 Significant Impact Levels (SILs) and significant Monitoring 

Concentration (SMC) were vacated by the United States Court of Appeals for the District of 

Columbia Circuit. EPA issued draft guidance for PM2.5 air quality impact assessments1 on March 

4, 2013. This guidance indicates that PSD compliance can be demonstrated in this case (direct 

emissions of PM2.5 do not trigger PSD review) via a screening-level analysis. 

In the companion document submitted with this assessment entitled “Background PM2.5

Analysis for the Eastern Gulf of Mexico Outer Continental Shelf”, ENVIRON provides a 

screening-level assessment of secondary PM2.5 impacts, and shows that sources such as 

Statoil’s are unlikely to adversely affect NAAQS compliance. Nonetheless, to provide an added 

level of conservatism, ENVIRON has retained the assessment of direct PM2.5 impacts in the 

original version of this document, and updated that assessment to reflect the addition 

information supplied after the original PSD application was submitted. 

ENVIRON applied computer-based dispersion modeling techniques to simulate dispersion of 

emissions attributable to the proposed exploration activities. The results of the modeling are 

 

1

 Available at http://www.epa.gov/ttn/scram/guidance/guide/Draft_Guidance_for_PM25_Permit_Modeling.pdf 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-2 

used to assess compliance with the PSD increments, the National Ambient Air Quality 

Standards (NAAQS) and Significance Impact Levels (SIL) for Class I and Class II areas. 

ENVIRON also used dispersion modeling techniques to assess Class I area PSD increments 

and degradation of regional visibility and other Air Quality Related Values (AQRVs). 

The dispersion modeling techniques employed in the analysis follow a basic set of EPA 

regulatory guidelines (40 CFR Part 51, Appendix W, revised November 9, 2005; referred to as 

the Guidelines). The Guidelines include recommendations for model selection, data 

preparation, and model application, but allow flexibility on a case-by-case basis. 

6.1 Dispersion Model Selection 

ENVIRON based its selection of the dispersion model on the characteristics of the proposed 

emission sources associated with the Maersk Developer and the Transocean Discoverer 

Americas drilling vessels and dispersion phenomena that might produce the maximum ground 

level concentrations. ENVIRON used the CALPUFF/CALMET modeling system to estimate 

impacts of air pollutants at discrete receptors placed 25 nautical miles from the States’ seaward 

boundary and at Class I areas, because of its design for long-range transport applications 

beyond 50 km. The modeling domain is shown in Figure 4 below as the blue box labeled 

“Statoil OCS CALPUFF Domain.” ENVIRON also used the VISCREEN model (Version 88341) 

to perform the visibility analysis for the Additional Impacts Analysis. VISCREEN calculates the 

potential impact of a plume of specified emissions for specific transport and dispersion 

conditions. 

A Good Engineering Practice (GEP) stack height analysis of the sources included in the 

modeling indicates building downwash would occur under some meteorological conditions. 

However, given that the nearest receptors are located about 100 km from the source, building 

downwash effects will not significantly affect the results and have been ignored. In general, at 

source-receptor distances this great, the details of the initial plume rise have an insignificant 

effect on the predicted concentrations. This is because the plume (puffs) have had time to 

disperse sufficiently to fill the planetary boundary layer (PBL, or mixing height). The details of 

stack exit velocity or temperature at various engine loads have an insignificant effect, and only 

the magnitude of emissions has a significant effect on predicted concentrations. 

6.2 Model Application 

ENVIRON applied CALPUFF using CALPUFF input parameters approved by EPA and the 

FWS. Note that EPA’s Mr. Stan Krivo requested that the Class I and Class II concentration 

assessments use a collection of CALPUFF control parameters that conflicts with the 

recommendation given in Appendix B of the IWAQM Report. He requested the concentration 

CALPUFF runs use MREG = MCHEM = MDRY = MWET = 0 (i.e. no chemistry, no deposition). 

ENVIRON understands that EPA has never officially accepted CALPUFF’s chemistry and 

deposition algorithms, but disagrees with this change in guidance and precedent. Nonetheless, 

in effort to expedite this permit application, ENVIRON has used the requested CALPUFF control 

parameters for all CALPUFF-predicted concentrations. Separate CALPUFF runs were 

generated for the FLMs as part of the AQRVs analysis. The FLMs have requested that 

CALPUFF be run with both chemistry and deposition to evaluate visibility impacts and 

deposition in the Class I areas. 
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Air Quality Impact Assessment 6-3 

6.2.1 Source Characterization 

The primary NOX and PM2.5 emission sources associated with the proposed exploration 

activities consist of diesel-fired engines on the drilling vessels. Additionally, the OCS air 

regulations define the OCS source to include direct emissions from vessels servicing the OCS 

sources while en route to or from the source when within 25 miles of the facility. These rules 

require Statoil to consider impacts from the associated fleet of vessels that support the drilling 

vessel. 

Developer emission sources include the following: 

 Main Generator Engines (8)

 Emergency Generator Engine (1)

 Cementing Unit Engines (2)

 Life Boats (4)

 Rescue Boat (1)

 Fuel Storage Vessels

 Fugitives (diesel fuel system)

 Support Vessels (e.g. crew boats) 

 Welding and Painting Activities

Discoverer Americas emission sources include the following: 

 Main Generator Engines (6)

 Emergency Generator Engine (1)

 Life Boats (6)

 Rescue Boat (1)

 Emergency Air Compressor Engines (2)

 Forklift Engines (2)

 Fuel Storage Vessels

 Fugitives (diesel fuel system)

 Support Vessels (e.g. crew boats)

 Welding, Cement/Mud Mixing, and Painting Activities

None of the associated vessels will have flare booms installed or conduct any flaring during the 

duration of the exploratory drilling operations. 

The basis for the maximum short-term and annual emission rates modeled for these sources 

are discussed in Section 6.2.4 below. 
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Air Quality Impact Assessment 6-4 

Figure 4 CALPUFF modeling domain (blue box), with “25 mile” receptors (red), Class I receptors (purple) and radii (light blue) LCC Northing, km
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-5 

6.2.2 Modeling Scenario 

Statoil is permitting the flexibility to use either the Maersk Developer or the Transocean 

Discoverer Americas drilling units at any given time to conduct exploratory drilling in the OCS of 

the Eastern Gulf of Mexico. Each drilling vessel and associated support vessels can operate 

under varying operating scenarios. 

Statoil considered multiple operating scenarios for each drilling vessel, including operations 

under a range of emissions and release parameters (including partial loads) and varying 

locations of associated support vessels. Because of the distance between the closest receptors 

and the emissions sources, ENVIRON concluded that maximum impacts would result from the 

highest short-term and long-term emission rate scenarios. 

For the short-term scenarios, this corresponds to the drilling vessels operating at maximum 

proposed load conditions. Note that this is not 100% load for each engine. The drilling vessel 

operators do not consider it safe to operate a single engine at 100% load, for fear of engine 

failure. They prefer to distribute the load between multiple engines for the sake of redundancy. 

Although these sources could operate at less than the maximum proposed load conditions, any 

changes in stack parameters resulting from the lower loads would not result in higher impacts at 

the modeled receptors, because the plume (puffs) are well-mixed within the PBL by the time 

they arrive at the receptors. 

For each of the two main drilling vessel scenarios (Maersk Developer or Transocean Discoverer 

Americas), Statoil has two sets of emission rates: short-term and long-term. 

The short-term emission rates are used for the following assessments: 

 Class II 1-hour NO2 SIL (NAAQS) 

 Class I & II 24-hour PM2.5 “SIL” (NAAQS & PSD Increment) 

 Class I visibility impairment 

The long-term emission rates are used for the remaining assessments: 

 Class II annual NO2 SIL (NAAQS & PSD Increment) 

 Class I & II annual PM2.5 “SIL” (NAAQS & PSD Increment) 

 Class I annual NO2 SIL 

 Class I annual Nitrogen deposition rate 

The EPA has not identified a regulatory-default model for secondary PM2.5. Therefore, only 

concentrations resulting from primary PM2.5 emissions will be compared to the (recently 

rescinded) PM2.5 SILs. The Developer maximum short-term emissions modeling analysis is 

based on five Main Generator engines operating at 60% load, auxiliary equipment (i.e., 

emergency generator engine, life boats, fast rescue boat and cementing unit engines) operating 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-6 

at 100% load and hourly emissions for support vessels (Crew Boats and Supply Boats) are 

derived from the maximum engine operation for the respective vessels. Annual emissions for 

the annual modeling analysis are based on three Main Generator engines operating at 60% 

load, all auxiliary equipment at 100% load, and support vessels based on maximum engine 

operation for the proposed annual run time. 

The Discoverer Americas maximum short-term emissions are based on four Main Generator 

engines operating at 80% load. The emergency generator engine operates at 70% load for 

testing purposes. Auxiliary equipment (i.e., emergency air compressor engines, forklift engines, 

life boats and fast rescue boat) operate at 100% load. Short-term support vessels (Crew Boats 

and Supply Boats) emission rates are derived from the maximum engine operating rates for the 

respective vessels. Annual emissions are based on three Main Generator engines operating at 

35% load and the emergency generator engine operating at 70% load. Annual emissions also 

include all other auxiliary equipment at 100% load, and support vessels based on maximum 

engine operation for the proposed annual run time. 

PM2.5 emissions from cement and mud mixing activities in support of Discoverer Americas 

operations were included in the modeling. NO2 and PM2.5 emissions from welding and painting 

activities on all vessels were determined to be insignificant2 and were not included in the 

assessment. 

Statoil is requesting authorization to allow the Maersk or the Transocean drilling vessels and 

their associated fleet to operate in any of Statoil’s lease blocks located within the eastern Gulf of 

Mexico. As such, Statoil represented worst-case dispersion conditions as follows: Each lease 

block has dimensions of approximately five kilometers by five kilometers. The closest point to 

shore is the northwest corner of the Desoto Canyon 143 lease block, which lies at 28.851o

N and 

87.424o

W. For purposes of this modeling analysis, Statoil modeled all scenarios from this 

northwest corner. This location has been selected to represent the lease blocks as a whole 

because it is the closest location to shore and the nearest Class I area (Breton Wilderness). 

Therefore, Statoil expects these to be the maximum model-predicted impacts. 

The locations of the associated support vessels (i.e, Crew Boats and Offshore Support 

Vessels [OSV]) also can affect the impacts at the receptors. In actual operations, support 

vessels are most likely either located adjacent to the drilling vessels with only minimal emissions 

associated with lower engine speeds, or arriving/departing from the drilling vessels with higher 

emissions associated with higher engine speeds. Statoil has therefore included one crew boat 

and one OSV in the modeling scenario, and modeled them as “under way” rather than at idle 

near the drilling vessel. The long-term emissions are based on the maximum hourly engine 

operation multiplied by the total number of hours of each vessel class. The short-term 

emissions are based on the vessels operating simultaneously at maximum load. 

For the annual averaging period and Class I visibility modeling, Statoil modeled the support 

vessels as a series of volume sources placed along a line originating at the drilling vessel and 

extending out 25 (nautical) miles in the direction of the vessel’s home port (Port Fourchon, 

 

2 Regulated air pollutants are less than 2 tpy and therefore insignificant per 40 CFR 71.5(c)(11)(ii). 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-7 

Louisiana). Modeling both support vessels’ emissions as a series of volume sources is 

conservative and appropriate for the maximum annual impacts.3

 

The line source algorithm in CALPUFF is essentially the same as the Buoyant Line Plume (BLP) 

model, which was developed to handle the unique situation of aluminum reduction plants. It is 

not appropriate for modeling the emissions of vessels underway. Instead, the emissions were 

distributed evenly among a series of ten (10) volume sources placed evenly along the line. 

Because the CALMET grid spacing is 4km, using a finer spacing would have little effect, as all 

the puffs originating within a grid box would “see” the same meteorology and be treated 

identically. 

For the short-term averaging period modeling, Statoil conservatively modeled the support 

vessels as stationary point sources. Both ships were assumed to be located at the same point, 

at the end of the 25-mile line closest to shore. Downwash was not included, because of the 

large distance to the nearest receptors which allows the puffs to expand to span the boundary 

layer – the details of the emissions points are not as important as the amount of emissions. 

All four of the Crew Boat’s main engines were assumed to be operating at 100% load, as were 

both of its generators. However, the Crew Boat bow thrusters were assumed to be not 

operating during transit. When the bow thruster engines are used the main engines are running 

at much lower loads, such that the total emissions for maneuvering are much smaller than 

during transit. Statoil also assumed the OSV emergency generator would not be operating 

during transit. 

Emissions attributable to cement handling and forklift operation were modeled as a volume 

source, centered on the main deck of the Discoverer Americas. 

A summary of the two sets of emission rates used in the modeling analyses by operating 

scenario is presented below. It should be noted that the maximum short-term emission rates 

are used to model 1-hour NO2 and 24-hour PM2.5 concentrations at the 25-mile and Class I 

receptors, and to assess changes in visibility at Class I area receptors. The maximum annual 

emission rates are used to assess annual-average NO2 and PM2.5 concentrations at the 25-mile 

and Class I receptors, and deposition rates at Class I area receptors. 

Developer 

 Maximum short-term (1-hour and 24-hour) emission rates: 

Five Main Generator engines at 60% load 

Auxiliary drilling vessel equipment (i.e., emergency generator, life boats, fast rescue boat 

and cementing unit engines) at 100% load 

OSV main engines at 100% load 

Crew boat main engines and generator engines at 100% load 

 Maximum annual emission rates: 

 

3

 Approach discussed and approved via the Protocol process. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-8 

Three Main Generator engines at 60% load 

Auxiliary drilling vessel equipment (i.e., emergency generator, life boats, fast rescue boat 

and cementing unit engines) at 100% load 

OSV and Crew vessels present, based on maximum annual operation 

Discoverer Americas

 Maximum short-term (1-hour & 24-hour) emission rates: 

Four Main Generator engines at 80% load 

Emergency Generator engine at 70% load (testing scenario) 

Auxiliary drilling vessel equipment (i.e., life boats, fast rescue boat, cement handling, forklift 

engines, and emergency air compressors) at 100% load 

OSV main engines at 100% load 

Crew boat main engines and generator engines at 100% load 

 Maximum annual emission rates: 

Three Main Generator engines at 35% load 

Emergency Generator engine at 70% load (testing scenario) 

Auxiliary drilling vessel equipment (i.e., life boats, fast rescue boat, cement handling, forklift 

engines, and emergency air compressors) at 100% load 

OSV and Crew vessels present, based on maximum annual operation 

6.2.3 Stack Parameters and Emission Rates 

In addition to emission rates, the modeling analysis requires information regarding stack 

heights, building dimensions, and other exit parameters that characterize exhaust flow from 

emission points. These release characteristics have an important influence on the results of the 

analysis. Ultimately, Statoil used emission rates corresponding to the selected worst-case 

impact operating scenarios discussed in Section 6.2.2. Statoil used the stack parameters such 

as stack heights and other exit parameters that characterize exhaust flow from emission points 

in the dispersion modeling simulations. 

For stacks with a vertical or ≥ 45° upward angled discharge, Statoil used available stack 

parameter data (i.e., stack diameter, stack exit velocity, and stack exit temperature). For stacks 

with horizontal discharges, Statoil adjusted the stack parameters to remove the plume rise due 

to momentum yet maintain thermal plume rise, by using a stack exit velocity of 0.001 meters per 

second (m/s). Stack heights are relative to the surface of the water. Exhaust stack parameters 

for the Developer and Discoverer Americas drilling vessels are listed in Tables 6.2.3-1 and 

Table 6.2.3-2, respectively. Support vessel exhaust stack parameters are listed in Table 

6.2.3-3. Stack parameters for emission sources modeled as volume sources for long-term and 

short-term scenarios are listed in Table 6.2.3-4 and Table 6.2.3-5, respectively. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-9 

Table 6.2.3-1

Developer Point Source Stack Parameters 

Used in CALPUFF Modeling Analysis 

Stack Modeling 

ID 

X-Coord Y-Coord Height Elev. Dia. Exit 

Vel. 

Exit 

Temp. Orientation 

(LCC) (LCC) (m) (m) (m) (m/s) (K) 

Gen. Engine 1 GEN1 941.93 -1186.23 28.93 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 2 GEN2 941.93 -1186.23 28.93 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 3 GEN3 941.93 -1186.23 26.82 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 4 GEN4 941.93 -1186.23 26.82 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 5 GEN5 941.93 -1186.3 28.93 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 6 GEN6 941.93 -1186.3 28.93 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 7 GEN7 941.93 -1186.3 26.82 0 0.8 0.001 623.15 Horizontal 

Gen. Engine 8 GEN8 941.93 -1186.3 26.82 0 0.8 0.001 623.15 Horizontal 

E. Gen Engine EGEN1 942.01 -1186.23 9.45 0 0.4 0.001 888.15 

Downward with 

45 degree angle 

to horizon 

Lifeboat 1 LB1 942.02 -1186.26 19.7 0 0.9 0.001 830.15 Horizontal 

Lifeboat 2 LB2 942.02 -1186.27 19.7 0 0.9 0.001 830.15 Horizontal 

Lifeboat 3 LB3 941.94 -1186.26 19.7 0 0.9 0.001 830.15 Horizontal 

Lifeboat 4 LB4 941.94 -1186.27 19.7 0 0.9 0.001 830.15 Horizontal 

MOB Engine 1 MOB1 941.93 -1186.26 19.7 0 1.9 0.001 773.15 Horizontal 

Cement Unit 

Engine 1 CMU1 941.98 -1186.3 9.45 0 0.2 0.001 794.15 

Downward with 

45 degree angle 

to horizon 

Cement Unit 

Engine 1 CMU2 941.98 -1186.3 9.45 0 0.2 0.001 794.15 

Downward with 

45 degree angle 

to horizon 

 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-10 

Table 6.2.3-2

Discoverer Americas Point Stack Parameters 

Used in CALPUFF Modeling Analysis 

Stack Modeling 

ID 

X-Coord Y-Coord Height Elev. Dia. Exit 

Vel. 

Exit 

Temp. Orientation 

(LCC) (LCC) (m) (m) (m) (m/s) (K) 

Gen. Engine 1 GEN1 941.853 -1186.259 21.33 0 1 0.001 640 Horizontal 

Gen. Engine 2 GEN2 941.852 -1186.261 21.33 0 1 0.001 640 Horizontal 

Gen. Engine 3 GEN3 941.853 -1186.262 21.33 0 1 0.001 640 Horizontal 

Gen. Engine 4 GEN4 941.853 -1186.268 21.33 0 1 0.001 640 Horizontal 

Gen. Engine 5 GEN5 941.852 -1186.269 21.33 0 1 0.001 640 Horizontal 

Gen. Engine 6 GEN6 941.853 -1186.271 21.33 0 1 0.001 640 Horizontal 

E-Gen. Engine EGEN 942.063 -1186.25 21.33 0 0.6 0.001 640 Horizontal 

Lifeboat 1 LB1 942.072 -1186.283 12.74 0 0.1 0.001 830.15 Horizontal 

Lifeboat 2 LB2 942.072 -1186.247 12.74 0 0.1 0.001 830.15 Horizontal 

Lifeboat 3 LB3 942.061 -1186.283 12.74 0 0.1 0.001 830.15 Horizontal 

Lifeboat 4 LB4 942.061 -1186.247 12.74 0 0.1 0.001 830.15 Horizontal 

Lifeboat 5 LB5 941.843 -1186.282 12.74 0 0.1 0.001 830.15 Horizontal 

Lifeboat 6 LB6 941.843 -1186.248 12.74 0 0.1 0.001 830.15 Horizontal 

MOB Engine 1 MOB 942.05 -1186.285 12.74 0 0.1 0.001 830.15 Horizontal 

Air Compressor 

1 ACOMP1 941.843 -1186.282 15.85 0 0 0.001 773 Horizontal 

Air Compressor 

2 ACOMP2 941.843 -1186.282 1.83 0 0 0.001 773 Horizontal 

Table 6.2.3-3

Support Vessel Point Source Stack Parameters 

Used in CALPUFF Modeling Analysis

Stack Modeling 

ID 

X-Coord 

(LCC) 

Y-Coord 

(LCC) 

Height 

(ft) 

Elev. 

(ft) 

Diameter 

(ft) 

Exit 

Velocity 

(ft/s) 

Exit 

Temp 

(K) 

Orientation 

OSV (Main #1) OSV1 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical 

OSV (Main #2) OSV2 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical 

OSV (Main #3) OSV3 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical 

OSV (Main #4) OSV4 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical 

Crewboats (Main 

#1) C1 895.858 -1186.624 3.28 0 1.00 188.32 718 Horizontal 

Crewboats (Main 

#2) C2 895.858 -1186.624 3.28 0 1.00 188.32 607 Horizontal 

Crewboats (Main 

#3) C3 895.858 -1186.624 3.28 0 1.00 188.32 607 Horizontal 

Crewboats (Main 

#4) C4 895.858 -1186.624 3.28 0 1.00 188.32 607 Horizontal 

Crewboats 

(Generator #1) CG1 895.858 -1186.624 3.28 0 0.33 152.25 610 Horizontal 

Crewboats 

(Generator #2) CG2 895.858 -1186.624 3.28 0 0.33 152.25 610 Horizontal 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-11 

The volume sources used in the annual simulations to simulate the crew boat and offshore 

support vessels within 25 miles of the drilling vessels require a height, elevation, and initial 

lateral (σy) and vertical (σz) dispersion parameters. The elevation was taken to be zero (mean 

sea level) and the volume height was set to the average of the Crew Boat and OSV heights: 

5.39 m and 33.42 m, respectively. The initial vertical dispersion Sigma-Z was taken as the 

average boat height divided by 2.15, and the initial horizontal dispersion Sigma-Y was 

calculated using the center-to-center distance between adjacent volume sources divided by 

2.15, following the guidance provided in EPA (1995)4

. 

The volume source used to represent the miscellaneous sources (cement handling and forklift 

usage aboard the Discoverer Americas) was assumed to be located on the drilling vessel’s main 

deck, 2.47 meters above water level. The initial plume height and Sigma-Z were based on an 

assumed height of 3m, and the initial Sigma-Y was assumed to be 10m. 

Maximum short-term (1-hour and 24-hour) and annual emission rates for these sources are 

summarized in Tables 6.2.3-6 through 6.2.3-19. 

 

4 ISCST3 Users Guide (EPA, 1995): Line source representation by adjacent volume sources. 

Table 6.2.3-4

Volume Source Stack Parameters for Support Vessels and Miscellaneous Sources 

Used in Visibility and Long-Term CALPUFF Modeling Analysis 

ID X-UTM Y- UTM Height (m) Elev (m) Sigma Y (m) Sigma Z (m) 

VOL01 895.858 -1186.62 19.41 0 2382 18.1 

VOL02 900.98 -1186.58 19.41 0 2382 18.1 

VOL03 906.101 -1186.55 19.41 0 2382 18.1 

VOL04 911.223 -1186.51 19.41 0 2382 18.1 

VOL05 916.345 -1186.47 19.41 0 2382 18.1 

VOL06 921.467 -1186.43 19.41 0 2382 18.1 

VOL07 926.589 -1186.39 19.41 0 2382 18.1 

VOL08 931.71 -1186.35 19.41 0 2382 18.1 

VOL09 936.832 -1186.31 19.41 0 2382 18.1 

VOL10 941.954 -1186.267 19.41 0 2382 18.1 

MISC (a) 941.964 -1186.269 1.5 2.74 10 1.4 

(a) MISC used to represent cement handling and the forklift, applicable only to the Discoverer Americas

Table 6.2.3-5 

Volume Source Stack Parameters for Miscellaneous Sources 

Used in Short-Term CALPUFF Modeling Analysis 

ID X-UTM Y- UTM Height (m) Elev (m) Sigma Y (m) Sigma Z (m) 

MISC (a) 941.964 -1186.269 1.5 2.74 10 1.4 

(a) MISC used to represent cement handling and the forklift, applicable only to the Discoverer Americas
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-12 

Table 6.2.3-6

Short-Term Emission Rates from Stacks 

Used in Developer CALPUFF Modeling 

Analysis

Source ID NOX (lb/hr) SO2 (lb/hr) PM2.5 (lb/hr) 

GEN1 53.53 0.04 0.98 

GEN2 53.53 0.04 0.98 

GEN3 53.53 0.04 0.98 

GEN4 53.53 0.04 0.98 

GEN5 53.53 0.04 0.98 

GEN6 0.00 0.00 0.00 

GEN7 0.00 0.00 0.00 

GEN8 0.00 0.00 0.00 

EGEN1 38.58 0.03 0.99 

LB1 0.36 0.0003 0.02 

LB2 0.36 0.0003 0.02 

LB3 0.36 0.0003 0.02 

LB4 0.36 0.0003 0.02 

MOB1 2.01 0.002 0.09 

CMU1 5.92 0.005 0.13 

CMU2 5.92 0.005 0.13 

Table 6.2.3-7

Short-term Speciated Emission Rates from Stacks 

Used in Developer CALPUFF Modeling Analysis

Source 

ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) 

NO3

(g/s) EC (g/s) SOA (g/s) 

PMC 

(g/s) 

PMF (a)

(g/s) 

GEN1 5.47E-03 2.97E-03 6.75E+00 0 1.54E-04 9.19E-02 2.78E-02 0 0 

GEN2 5.47E-03 2.97E-03 6.75E+00 0 1.54E-04 9.19E-02 2.78E-02 0 0 

GEN3 5.47E-03 2.97E-03 6.75E+00 0 1.54E-04 9.19E-02 2.78E-02 0 0 

GEN4 5.47E-03 2.97E-03 6.75E+00 0 1.54E-04 9.19E-02 2.78E-02 0 0 

GEN5 5.47E-03 2.97E-03 6.75E+00 0 1.54E-04 9.19E-02 2.78E-02 0 0 

GEN6 0 0 0 0 0 0 0 0 0 

GEN7 0 0 0 0 0 0 0 0 0 

GEN8 0 0 0 0 0 0 0 0 0 

EGEN1 3.49E-03 2.99E-03 4.86E+00 0 1.55E-04 9.27E-02 2.81E-02 0 0 

LB1 3.97E-05 6.88E-05 4.51E-02 0 3.57E-06 2.13E-03 6.45E-04 0 0 

LB2 3.97E-05 6.88E-05 4.51E-02 0 3.57E-06 2.13E-03 6.45E-04 0 0 

LB3 3.97E-05 6.88E-05 4.51E-02 0 3.57E-06 2.13E-03 6.45E-04 0 0 

LB4 3.97E-05 6.88E-05 4.51E-02 0 3.57E-06 2.13E-03 6.45E-04 0 0 

MOB1 2.23E-04 2.58E-04 2.53E-01 0 1.34E-05 7.98E-03 2.42E-03 0 0 

CMU1 6.85E-04 3.95E-04 7.46E-01 0 2.05E-05 1.22E-02 3.71E-03 0 0 

CMU2 6.85E-04 3.95E-04 7.46E-01 0 2.05E-05 1.22E-02 3.71E-03 0 0 

(a) Speciation above provided for CALPUFF visibility runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-13 

Table 6.2.3-8

Long-Term Emission Rates From Stacks 

Used In Developer CALPUFF Modeling 

Analysis

Source ID NOX (tpy) SO2 (tpy) PM2.5 (tpy) 

GEN1 115.63 0.09 2.13 

GEN2 115.63 0.09 2.13 

GEN3 115.63 0.09 2.13 

GEN4 0 0 0 

GEN5 0 0 0 

GEN6 0 0 0 

GEN7 0 0 0 

GEN8 0 0 0 

EGEN1 0.76 0.007 0.02 

LB1 0.002 0.000002 0.0001 

LB2 0.002 0.000002 0.0001 

LB3 0.002 0.000002 0.0001 

LB4 0.002 0.000002 0.0001 

MOB1 0.01 0.00001 0.0005 

CMU1 0.18 0.0002 0.004 

CMU2 0.18 0.0002 0.004 

Table 6.2.3-9

Long-Term Speciated Emission Rates from Stacks 

Used in Developer CALPUFF Modeling Analysis

Source 

ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) NO3 (g/s) EC (g/s) SOA (g/s) 

PMC

(g/s) 

PMF (a)

(g/s) 

GEN1 2.70E-03 1.46E-03 3.33E+00 0 7.58E-05 4.53E-02 1.37E-02 0 0 

GEN2 2.70E-03 1.46E-03 3.33E+00 0 7.58E-05 4.53E-02 1.37E-02 0 0 

GEN3 2.70E-03 1.46E-03 3.33E+00 0 7.58E-05 4.53E-02 1.37E-02 0 0 

GEN4 0 0 0 0 0 0 0 0 0 

GEN5 0 0 0 0 0 0 0 0 0 

GEN6 0 0 0 0 0 0 0 0 0 

GEN7 0 0 0 0 0 0 0 0 0 

GEN8 0 0 0 0 0 0 0 0 0 

EGEN1 1.57E-05 1.35E-05 2.19E-02 0 6.99E-07 4.18E-04 1.26E-04 0 0 

LB1 5.44E-08 9.42E-08 6.17E-05 0 4.88E-09 2.92E-06 8.84E-07 0 0 

LB2 5.44E-08 9.42E-08 6.17E-05 0 4.88E-09 2.92E-06 8.84E-07 0 0 

LB3 5.44E-08 9.42E-08 6.17E-05 0 4.88E-09 2.92E-06 8.84E-07 0 0 

LB4 5.44E-08 9.42E-08 6.17E-05 0 4.88E-09 2.92E-06 8.84E-07 0 0 

MOB1 3.06E-07 3.53E-07 3.47E-04 0 1.83E-08 1.09E-05 3.31E-06 0 0 

CMU1 4.69E-06 2.71E-06 5.11E-03 0 1.40E-07 8.39E-05 2.54E-05 0 0 

CMU2 4.69E-06 2.71E-06 5.11E-03 0 1.40E-07 8.39E-05 2.54E-05 0 0 

(a) Speciation above provided for CALPUFF deposition runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-14 

Table 6.2.3-10

Short-Term Emission Rates From Stacks Used 

In Discoverer Americas CALPUFF Modeling 

Analysis

Source ID NOX (lb/hr) SO2 (lb/hr) PM2.5 (lb/hr) 

GEN1 127.04 0.08 1.85 

GEN2 127.04 0.08 1.85 

GEN3 127.04 0.08 1.85 

GEN4 127.04 0.08 1.85 

GEN5 0 0 0 

GEN6 0 0 0 

EGEN 42.31 0.02 0.84 

LB1 0.44 0.0004 0.03 

LB2 0.44 0.0004 0.03 

LB3 0.44 0.0004 0.03 

LB4 0.44 0.0004 0.03 

LB5 0.44 0.0004 0.03 

LB6 0.44 0.0004 0.03 

MOB 2.61 0.002 0.11 

ACOMP1 0.78 0.0003 0.05 

ACOMP2 1.05 0.0004 0.07 

Table 6.2.3-11

Short-Term Speciated Emission Rates From Stacks 

Used In Discoverer Americas CALPUFF Modeling Analysis

Source ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) NO3 (g/s) EC (g/s) SOA (g/s) 

PMC 

(g/s) 

PMF (a)

(g/s) 

GEN1 1.03E-02 5.58E-03 1.60E+01 0 2.89E-04 1.73E-01 5.24E-02 0 0 

GEN2 1.03E-02 5.58E-03 1.60E+01 0 2.89E-04 1.73E-01 5.24E-02 0 0 

GEN3 1.03E-02 5.58E-03 1.60E+01 0 2.89E-04 1.73E-01 5.24E-02 0 0 

GEN4 1.03E-02 5.58E-03 1.60E+01 0 2.89E-04 1.73E-01 5.24E-02 0 0 

GEN5 0 0 0 0 0 0 0 0 0 

GEN6 0 0 0 0 0 0 0 0 0 

EGEN 2.97E-03 2.54E-03 5.33E+00 0 1.32E-04 7.88E-02 2.39E-02 0 0 

LB1 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

LB2 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

LB3 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

LB4 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

LB5 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

LB6 4.93E-05 8.54E-05 5.59E-02 0 4.43E-06 2.65E-03 8.01E-04 0 0 

MOB 2.90E-04 3.35E-04 3.29E-01 0 1.74E-05 1.04E-02 3.14E-03 0 0 

ACOMP1 3.42E-05 1.61E-04 9.76E-02 0 8.34E-06 4.98E-03 1.51E-03 0 0 

ACOMP2 4.66E-05 2.19E-04 1.33E-01 0 1.13E-05 6.78E-03 2.05E-03 0 0 

(a) Speciation above provided for CALPUFF visibility runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-15 

Table 6.2.3-12

Long-Term Emission Rates From Stacks Used In 

Discoverer Americas CALPUFF Modeling Analysis

Source ID NOX (tpy) SO2 (tpy) PM2.5 (tpy) 

GEN1 140.8 0.08 1.75 

GEN2 140.8 0.08 1.75 

GEN3 140.8 0.08 1.75 

GEN4 0 0 0 

GEN5 0 0 0 

GEN6 0 0 0 

EGEN 0.88 0.0005 0.02 

LB1 0.003 0.000002 0.0002 

LB2 0.003 0.000002 0.0002 

LB3 0.003 0.000002 0.0002 

LB4 0.003 0.000002 0.0002 

LB5 0.003 0.000002 0.0002 

LB6 0.003 0.000002 0.0002 

MOB 0.02 0.00001 0.0007 

ACOMP1 0.002 8.15E-7 0.00016 

ACOMP2 0.003 1.11E-6 0.00022 

Table 6.2.3-13

Long-Term Speciated Emission Rates From Stacks Used In 

Discoverer Americas CALPUFF Modeling Analysis

Source 

ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) 

NO3

(g/s) 

EC 

(g/s) 

SOA 

(g/s) 

PMC

 (g/s) 

PMF (a)

 (g/s) 

GEN1 2.22E-03 1.20E-03 4.05E+00 0 6.24E-05 3.73E-02 1.13E-02 0 0 

GEN2 2.22E-03 1.20E-03 4.05E+00 0 6.24E-05 3.73E-02 1.13E-02 0 0 

GEN3 2.22E-03 1.20E-03 4.05E+00 0 6.24E-05 3.73E-02 1.13E-02 0 0 

GEN4 0 0 0 0 0 0 0 0 0 

GEN5 0 0 0 0 0 0 0 0 0 

GEN6 0 0 0 0 0 0 0 0 0 

EGEN 1.40E-05 1.20E-05 2.52E-02 0 6.23E-07 3.73E-04 1.13E-04 0 0 

LB1 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

LB2 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

LB3 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

LB4 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

LB5 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

LB6 6.75E-08 1.17E-07 7.66E-05 0 6.06E-09 3.62E-06 1.10E-06 0 0 

MOB 3.98E-07 4.59E-07 4.51E-04 0 2.38E-08 1.42E-05 4.31E-06 0 0 

ACOMP1 2.35E-08 1.10E-07 6.69E-05 0 5.71E-09 3.41E-06 1.03E-06 0 0 

ACOMP2 3.19E-08 1.50E-07 9.10E-05 0 7.77E-09 4.64E-06 1.41E-06 0 0 

(a) Speciation above provided for CALPUFF deposition runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-16 

Table 6.2.3-14

Short-Term Emission Rates from Stacks Used in 

Support Vessel CALPUFF Modeling Analysis

Source ID NOX (lb/hr) SO2 (lb/hr) PM2.5 (lb/hr) 

OSV1 42.41 0.03 0.92 

OSV2 42.41 0.03 0.92 

OSV3 42.41 0.03 0.92 

OSV4 42.41 0.03 0.92 

C1 21.30 0.02 0.47 

C2 21.30 0.02 0.47 

C3 21.30 0.02 0.47 

C4 21.30 0.02 0.47 

CG1 1.48 0.00 0.05 

CG2 1.48 0.00 0.05 

Table 6.2.3-15 

Short-term Speciated Emission Rates from Stacks 

Used in Support Vessel CALPUFF Modeling Analysis

Source ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) NO3 (g/s) EC (g/s) SOA (g/s) 

PMC 

(g/s) 

PMF (a)

(g/s) 

OSV1 3.24E-03 2.78E-03 5.34E+00 0 1.44E-04 8.60E-02 2.60E-02 0 0 

OSV2 3.24E-03 2.78E-03 5.34E+00 0 1.44E-04 8.60E-02 2.60E-02 0 0 

OSV3 3.24E-03 2.78E-03 5.34E+00 0 1.44E-04 8.60E-02 2.60E-02 0 0 

OSV4 3.24E-03 2.78E-03 5.34E+00 0 1.44E-04 8.60E-02 2.60E-02 0 0 

C1 2.46E-03 1.42E-03 2.68E+00 0 7.37E-05 4.41E-02 1.33E-02 0 0 

C2 2.46E-03 1.42E-03 2.68E+00 0 7.37E-05 4.41E-02 1.33E-02 0 0 

C3 2.46E-03 1.42E-03 2.68E+00 0 7.37E-05 4.41E-02 1.33E-02 0 0 

C4 2.46E-03 1.42E-03 2.68E+00 0 7.37E-05 4.41E-02 1.33E-02 0 0 

CG1 1.71E-04 1.48E-04 1.86E-01 0 7.67E-06 4.58E-03 1.39E-03 0 0 

CG2 1.71E-04 1.48E-04 1.86E-01 0 7.67E-06 4.58E-03 1.39E-03 0 0 

(a) Speciation above provided for CALPUFF visibility runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-17 

Table 6.2.3-16

Long-Term Emission Rates From Stacks Used In 

Support Vessel CALPUFF Modeling Analysis

Source ID NOX (tpy) SO2 (tpy) PM2.5 (tpy) 

OSV1 54.49 0.03 1.18 

OSV2 54.49 0.03 1.18 

OSV3 0.00 0.00 0.00 

OSV4 0.00 0.00 0.00 

C1 6.58 0.01 0.15 

C2 6.58 0.01 0.15 

C3 6.58 0.01 0.15 

C4 6.58 0.01 0.15 

CG1 0.46 0.00 0.02 

CG2 0.46 0.00 0.02 

Table 6.2.3-17

Long-Term Speciated Emission Rates from Stacks 

Used in Support Vessel CALPUFF Modeling Analysis

Source 

ID SO2 (g/s) SO4 (g/s) NOx (g/s)

HNO3

(g/s) NO3 (g/s) EC (g/s) SOA (g/s)

PMC 

(g/s)

PMF (a)

(g/s)

OSV1 9.51E-04 8.15E-04 1.57E+00 0 4.22E-05 2.52E-02 7.64E-03 0 0 

OSV2 9.51E-04 8.15E-04 1.57E+00 0 4.22E-05 2.52E-02 7.64E-03 0 0 

OSV3 0 0 0 0 0 0 0 0 0 

OSV4 0 0 0 0 0 0 0 0 0 

C1 1.74E-04 1.00E-04 1.89E-01 0 5.20E-06 3.11E-03 9.42E-04 0 0 

C2 1.74E-04 1.00E-04 1.89E-01 0 5.20E-06 3.11E-03 9.42E-04 0 0 

C3 1.74E-04 1.00E-04 1.89E-01 0 5.20E-06 3.11E-03 9.42E-04 0 0 

C4 1.74E-04 1.00E-04 1.89E-01 0 5.20E-06 3.11E-03 9.42E-04 0 0 

CG1 1.21E-05 1.04E-05 1.31E-02 0 5.41E-07 3.23E-04 9.79E-05 0 0 

CG2 1.21E-05 1.04E-05 1.31E-02 0 5.41E-07 3.23E-04 9.79E-05 0 0 

(a) Speciation above provided for CALPUFF deposition runs, but EPA runs assumed all PM2.5 emitted as PMF. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-18 

Table 6.2.3-18

Short-Term Emission Rates From Volume Sources Used In Discoverer Americas

CALPUFF Modeling Analysis

Source ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3

(g/s) 

NO3 

(g/s) 

EC 

(g/s) 

SOA 

(g/s) 

PMC 

(g/s) 

PMF (a)

(g/s) 

Forklift 1.37E-04 0 9.74E-02 0 0 0 0 0 2.48E-03 

Cement 0 0 0 0 0 0 0 0 4.77E-02 

MISC (sum) 5.26E-02 

(a) All PM2.5 assumed emitted as PMF.

Table 6.2.3-19

Long-Term Emission Rates From Volume Sources Used In Discoverer Americas

CALPUFF Modeling Analysis

Source ID SO2 (g/s) SO4 (g/s) NOx (g/s) 

HNO3 

(g/s) 

NO3

(g/s) 

EC 

(g/s) 

SOA 

(g/s) 

PMC 

(g/s) 

PMF (a)

(g/s) 

Forklift 1.86E-06 0 1.31E-02 0 0 0 0 0 6.69E-05 

Cement 0 0 0 0 0 0 0 0 2.35E-05 

MISC (sum) 2.36E-02 

(a) All PM2.5 assumed emitted as PMF.
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-19 

6.2.4 Building Downwash (Prime Algorithm) 

Building downwash is the effect of nearby structures on the flow of emissions from their 

respective sources. However, as discussed in Section 6.1, ENVIRON did not account for 

building downwash effects as part of the 25-mile receptor modeling approach. Given that the 

nearest receptors are located about 100 km from the source, building downwash effects will not 

significantly affect the modeled results. The FLMs typically do not request downwash be 

included, and neither “downwash” nor “BPIP” are mentioned in either FLAG (2000) or FLAG 

(2010). 

6.2.5 Receptor Locations 

EPA has established a policy for EGOM of using receptors placed 25 nautical miles from the 

nearby States’ seaward boundaries. These discrete 25-mile receptors were generated using 

the State seaward boundaries for Louisiana, Mississippi, Alabama, and Florida. The boundaries 

extend for up to the three nautical miles for Louisiana, Mississippi and Alabama and up to nine 

nautical miles for Florida5

. ENVIRON placed discrete receptors approximately 1 km apart. The 

location of these receptors is shown in Figure 4 above as red dots (Note: receptors may appear 

as a solid red line in Figure 4 due to low resolution). All these receptors are over water. 

Therefore, terrain elevations were not used for the Class II analysis: all receptors were assigned 

an elevation of 0 m (i.e., sea level). 

6.2.6 Meteorological Data 

Statoil used a three-year meteorological CALMET dataset (2001 – 2003) which was prepared 

for the Visibility Improvement State and Tribal Association of the Southeast (VISTAS) – Best 

Available Retrofit Technology (BART) modeling. Specifically, the 4-km VISTAS Domain 2 

dataset was used for the modeling analysis, for both the Class I and Class II assessments. The 

three year CALPUFF-ready meteorological dataset was provided by the North Carolina 

Department of Environment and Natural Resources (NC DENR). This is the most recent 

version developed by the FLMs, using the currently approved regulatory version of CALMET 

(Version 5.8, level 070623). The CALPUFF computational grid was taken to be a subset of the 

full VISTAS grid, using points 1 to 186 in the X direction (East) and points 56 to 163 in the Y 

direction (North). This sub-domain, along with the full VISTAS domain, is shown in Figure 4, 

and includes a 50 km buffer past the Class I area. The domain was extended far enough to the 

East to include the 25-mile receptors along Western Florida, and far enough South to include a 

100 km buffer around the drill rig location to allow for re-circulation of puffs. 

6.3 Project Impact Assessment 

This section assesses the magnitude of concentration impacts resulting from emissions from the 

proposed Statoil exploration activities at the discrete 25-mile receptors. If a pollutant’s 

calculated concentration exceeds the EPA SIL for that pollutant, the impacts of the facility must 

be assessed in the context of other increment-consuming sources to evaluate total increment 

consumption. Exceeding a SIL also requires that the facility’s compliance with the applicable 

NAAQS be evaluated, taking into account background concentrations and the contributions of 

significant regional sources. 

 

5

 U. S. Commission on Ocean Policy. Primer on Ocean Jurisdictions: Drawing Lines in the Water. Final Report. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-20 

The attached report summarizes PM2.5 in the EGOM region. It provides support for the use of 

the PM2.5 SILs (for sources that exceed the PSD Significant Emission Rate for PM2.5, which is 

not the case in this application) and provides a summary of data to be used in lieu of preconstruction monitoring data. It also contains a qualitative discussion of secondary PM2.5 that 

may arise from NOX/SO2 emissions originating in the EGOM. Although the attached report is 

not specific to Statoil’s proposed emissions, it shows that emissions in the range of those 

covered by this PSD permit application are not likely to cause or contribute to an exceedance of 

the PM2.5 NAAQS on shore. 

As discussed previously, ENVIRON applied the CALPUFF/CALMET modeling system to 

simulate pollutant dispersion for three years of hourly meteorological data. ENVIRON 

determined the highest concentrations for each discrete receptor. This section discusses the 

results of the modeling assessment. 

6.3.1 Class II Criteria Pollutant Concentrations 

ENVIRON modeled the criteria pollutant concentrations using the emission rates presented 

above in Tables 6.2.3-6 through 6.2.3-8 and Tables 6.2.3-9 through 6.2.3-12 for Developer and 

Discoverer Americas drilling vessels, respectively, for comparison to the SIL and SMC for NO2

6

. 

Although the SILs and SMC for PM2.5 have been vacated, we present the PM2.5 results and 

compare them to the (former) SILs as an added level of conservatism. 

In order to assess the significance of the predictions, ENVIRON compared the 3-year average 

maximum NO2 concentrations at the discrete 25-mile receptors predicted by CALPUFF with the 

Class II PSD SIL for NO2. NOx was assumed to be 80% converted to NO2, consistent with a 

“Tier 2” approach. ENVIRON also compared the maximum PM2.5 concentrations to the Class II 

PSD SIL for PM2.5. Although the PSD SIL and SMC for PM2.5 were recently rescinded, they are 

deemed appropriate as measures of significance in this case. Justification for this decision is 

found in the attached report, “Background PM2.5 Analysis for the Eastern Gulf of Mexico Outer 

Continental Shelf”. These Class II receptors with concentrations below the SILs are considered 

to be “insignificantly affected” and these pollutants do not require assessments of the Class II 

increments or NAAQS. 

ENVIRON compared the maximum criteria pollutant concentrations at the discrete 25-mile 

receptors predicted by CALPUFF with the applicable SMC for NO2 and PM2.5. If the highest 

modeled concentration caused by the proposed significant emissions increase is above the 

SMC, then a demonstration of pre-construction ambient NO2 or PM2.5 levels would be required. 

However, no monitoring is required if modeling results of the significance analysis are below the 

defined SMC for NO2 and PM2.5. 

 

6

 It has been EPA's longstanding policy under the New Source Review and PSD programs to allow the use of 

Significant Impact Levels (SILs) to assess whether a proposed new or modified stationary source causes or 

contributes to a violation of the NAAQS or PSD Class II increments (40 CFR 51.165 (b)(2)). Sources with pollutant 

concentrations under the SILs are considered insignificant, whether or not background or other increment 

consuming sources affect the applicable pollutant concentration and averaging period of concern. The SIL criteria 

are only intended to apply to the ambient standards and Class II increments, not the Class I increments or the need 

to conduct an AQRV analysis (see, for example, Calcagni, 1991). Note that the use of the term "significant" impact 

level in the PSD program does not imply a “significant adverse impact” in a NEPA sense, nor does it imply 

exceedances of ambient standards established to protect health and welfare. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-21 

The results of the CALPUFF modeling analysis are compared to the applicable SILs and SMCs 

in Table 6.3.1-1. Because the maximum predicted concentrations on 1-hour, 24-hour, and 

annual average are less than the applicable SILs, the project is deemed to not cause or 

contribute to a violation of the NAAQS or PSD increments for these pollutants. Furthermore, the 

maximum predicted NO2 concentrations are less than the applicable SMC; therefore, no 

monitoring is required. 

Table 6.3.1-1 

Maximum CALPUFF-Predicted Class II Concentrations 

Criteria 

Pollutant 

Averaging 

Period 

Developer 

Max. 

Concentration

(μg/m3)

Discoverer 

Americas Max. 

Concentration

(μg/m3)

Modeling 

Significance 

Level 

(μg/m3) 

Monitoring 

DeMinimus 

Concentration 

(μg/m3) 

NO2 a 1-hr 5.7 7.3 7.5 c

 None c

Annual 0.03 0.04 1.0 14 

PM2.5

24-hr b

 0.08 0.10 1.2 d 4 d

Annual 0.0009 0.0008 0.3 d None 

Notes: a

 Annual NOX was assumed to be 75 percent converted to NO2. One-hour NO2 model prediction based on the three year 

average of the maximum daily model-predicted 1-hour NOX concentration at each receptor location and 80 percent conversion 

to NO2 (Tier II of EPA’s June 28, 2010 memo “Guidance Concerning the Implementation of the 1-hour NO2 NAAQS for the 

Prevention of Significant Deterioration Program.”

b 100th percentile (maximum) values are presented (not 98th percentile) using direct PM2.5 emissions only. 

c

 Interim SIL, established June 28, 2010 in the memo “Guidance Concerning the Implementation of the 1-hour NO2 NAAQS for 

the Prevention of Significant Deterioration Program”. The 1-hour NO2 Monitoring DeMinimus level has not yet been proposed.

d

 The PM2.5 SILs and SMC were vacated on January 22, 2013,but presented here for comparison. 

 

6.4 Class I Air Quality Related Values Analysis 

PSD guidance requires an analysis of potential impacts to AQRVs in Federal Class I areas 

within 100 km (62.1 miles) of the facility from pollutants emitted by the project subject to PSD 

review. However, Federal Land Managers (FLMs) typically request analyses of AQRV impacts 

for Class I areas within 200 km (124 miles) of the site. Best Available Retrofit 

Technology (BART) exemption and determination modeling under EPA’s Regional Haze 

Regulations require that Class I areas within 300 km (186 miles) be included. A larger domain 

similar to that developed for BART modeling was used for this analysis, resulting in the inclusion 

of Class I areas beyond those usually required for a PSD analysis. Figure 4 presented above 

documents the CALPUFF modeling domain with the selected Class I area. 

As shown previously in Figure 4, there is one Class I area within 300 km of the facility. The 

nearest Class I area, the Breton Wilderness Area, is located at a distance of 175 km (109 miles) 

from the nearest proposed OCS Project lease block area. Statoil contacted the FWS to discuss 

the proposed OCS Project and AQRV analysis. Statoil also submitted the modeling protocol to 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-22 

the FWS on July 23, 2012, which was subsequently approved on July 30, 2012.7 The distances 

from the proposed Statoil exploration activities to the four closest Class I areas considered in 

this analysis are listed in Table 6.4-1. 

Table 6.4-1 

Nearest Distance to Class I Area from Proposed Project 

ID Class I Area Distance1 (Km) 

BRET Breton Wilderness Area 175 

BRBA Bradwell Bay Wilderness Area 307 

STMA Saint Marks Wilderness Area 313 

CHAS Chassahowitzka Wilderness Area 641 

Notes: 

a Distance to the northwest corner of Desoto Canyon 143 lease block (28.85064o

N and 

87.42378oW) 

The Breton, Chassahowitzka, and Saint Marks Wilderness Areas are managed by the FWS. 

The Bradwell Bay Wilderness Area is managed by the FS. The AQRVs of concern include 

visibility, soil, flora, fauna, and aquatic resources. The CALPUFF modeling system is currently 

recommended for evaluating impacts to AQRVs in Class I areas affected by long-range 

transport. Potential impacts are characterized based on predictions of total nitrogen and/or 

sulfur deposition flux, change in light extinction, and pollutant concentrations. Pollutant 

concentration predictions were also used to assess Class I area increment consumption for 

pollutants subject to PSD review. 

6.4.1 Model Selection 

On April 15, 2003, EPA adopted the CALPUFF modeling system as the EPA’s preferred model 

for long-range transport assessments and for evaluating potential impacts to Class I areas by 

including CALPUFF in Appendix A of the Guidelines. Features of the CALPUFF modeling 

system include the ability to consider: secondary aerosol formation; gaseous and particle 

deposition; wet and dry deposition processes; complex three-dimensional wind regimes; and the 

effects of humidity on regional visibility. As is currently required, CALPUFF Version 5.8 (release 

date June 23, 2007) was used; except for CALPOST, for which version 6.221 (release date July 

24, 2008) was used8

. 

6.4.2 Modeling Procedures 

The modeling procedures used for the Class I area analyses followed the recommendations of 

the Interagency Agency Workgroup on Air Quality Modeling (IWAQM) and the FLM Air Quality 

Related Values Workgroup (FLAG), outlined in the FLAG Phase I Report - Revised (November 

10, 2010). EPA endorsed these procedures in advance of the IWAQM Phase II report 

(December 1998), and reiterated this endorsement in the April 15, 2003 Federal Register notice 

(Volume 68, Number 72) that adopted CALPUFF as a Guideline model. EPA further clarified 

 

7

 Email correspondence from Jill Webster, dated July 30, 2012. 

8

 See http://www.epa.gov/ttn/scram/dispersion_prefrec.htm#calpuff 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-23 

their required CALMET setting in a memo issued on August 31, 2009 (Fox 2009).9 However, 

EPA’s Mr. Stan Krivo requested that the CALPUFF runs used to assess Increment (SILs) use 

no chemical transformation or deposition. Statoil therefore performed two sets of CALPUFF 

runs, one following the IWAQM Phase II report (MCHEM = MDRY = MWET = 1) for the FLMs, 

to assess visibility degradation and S/N deposition; and one contradicting IWAQM (MCHEM = 

MDRY = MWET = 0) for the EPA to assess Class I SILs for Increment. 

6.4.3 Model Setup and Application 

The CALPUFF modeling system is equipped with a host of modeling options, but, as stated in 

the previous section, ENVIRON used the procedures and defaults recommended by the FLAG 

Phase I Report. Any deviations from the defaults were approved by the FLM. CALPUFF control 

parameters are listed in Appendix A of the Modeling Protocol. 

For the regional haze assessment using the CALPUFF modeling system, particulate matter 

emission rates must be speciated into six fractions: soot or elemental carbon (EC), PM fine 

(PMF), PM coarse (PMC), organic carbon (OC), sulfate (SO4), and nitrate (NO3). Tables 

provided in Section 6.2.3 presented the speciated particulate matter emission rates used in the 

analysis. The speciation was based on speciation profiles recommended for aerosol modeling 

by the EPA.10 Sources in the database are referenced by Source Classification Code (SCC), 

and the database provided information for speciating the fine fraction into the other components 

required by CALPUFF. All the emission units are diesel-fired and appropriate SCC codes were 

chosen. 

The CALPUFF modeling conservatively used the maximum short-term emission rate (1-hour) 

for the short-term assessment assessments. As previously discussed, the maximum short-term 

emission rates for support vessels are based on maximum engine operation for the entire 24-

hour period. Maximum short-term emission rates for main engines on the drill rigs are based on 

maximum expected hourly operating loads, as discussed in Section 6.2.3. 

6.4.4 Averaging Periods 

CALPUFF-predicted hourly pollutant concentrations were averaged for comparison with 

applicable 1-hour and annual NO2 and 24-hour and annual PM2.5 Class I SILs and PSD 

increments. Predicted extinction coefficients and total deposition fluxes were calculated as 24-

hour and annual averages, respectively. In all instances, comparisons with regulatory criteria 

were based on the highest model-prediction of the three-year simulation for the averaging 

period. 

6.4.5 Chemical Transformations 

The NOX chemistry in CALPUFF depends on the ambient ammonia concentration to establish 

the equilibrium between gaseous nitric acid and ammonium nitrate. However, ambient 

ammonia concentrations are not explicitly simulated by CALPUFF and the user must select an 

appropriate background concentration. The IWAQM Phase II Recommendations suggest 

typical ammonia concentrations as: 10 parts per billion (ppb) for grasslands, 0.5 ppb for forests, 

 

9

 USEPA Memorandum. Clarification on EPA-FLM Recommended Settings for CALMET. August 2009. 

http://www.epa.gov/ttn/scram/CALMET%20CLARIFICATION.pdf 10 USEPA website containing PM speciation for source categories: http://www.epa.gov/ttn/chief/emch/speciation. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-24 

and 1 ppb for arid lands during warmer weather. Given the low background concentration over 

the Gulf of Mexico and as requested by the FLM, ENVIRON used a background ammonia 

concentration of 3 ppb. 

Reaction rates in the CALPUFF chemistry algorithms are also influenced by background ozone 

concentrations. ENVIRON used hourly ozone data for 2001-2003 to represent background 

ozone concentrations for the modeled years. This data was included in the VISTAS CALMET 

data. CALPUFF uses a background ozone value (BCK03) for hours when none of the supplied 

ozone stations have valid data. A conservative value of 65 ppb was specified, to avoid 

artificially limiting chemical transformations (e.g. NOX titration). 

6.4.6 Domain and Receptors 

The domain for the CALPUFF simulations is shown in Figure 4. The 740 km-by-428 km domain 

is large enough to include the Class I areas of interest with at least a 50 km allowance for 

complex flows that might cause recirculation of plumes originating at the lease block Desoto 

Canyon (DC) 143. A Lambert Conformal Coordinate (LCC) system was used for the 

coordinates. 

The CALPUFF dispersion model simulations assessed AQRVs at discrete receptors obtained 

from the National Park Service11, and include elevations ranging from 0.021 to 0.375 m. 

Figure 4 also shows the discrete receptor locations within the Breton Class I area. Gridded 

receptors were turned off in the CALPUFF runs to make the runtimes more reasonable. 

6.4.7 Emission Rates and Stack Parameters 

Modeled emission rates are discussed in Section 6.2.3 above. 

6.4.8 Meteorological Data 

Preprocessed VISTAS - BART 4 km Domain 2 CALMET data was used for modeling. This data 

was provided by the North Carolina Department of Environment and Natural Resources 

(NCDENR). Data from 109 surface stations, 10 upper air stations, 9 overwater stations and 96 

precipitation stations was used to process the 2001 CALMET data. Data from 100 surface 

stations, 10 upper air stations, 9 overwater stations and 92 precipitation stations was used to 

process the 2002 CALMET data. Data from 116 surface stations, 10 upper air stations, 9 

overwater stations and 103 precipitation stations was used to process the 2003 CALMET data. 

This is the most recent version developed by the FLM using the currently approved regulatory 

version of CALMET (Version 5.8). For the current analysis the 4-km mesh size simulations 

were used in order to better resolve the flow in the complex terrain. 

CALMET (Version 5.8), the meteorological preprocessor component of the CALPUFF system, 

was used to combine the MM5 simulation data, surface observations, terrain elevations, and 

land use data into the format required by the dispersion modeling component CALPUFF. In 

addition to specifying the three-dimensional wind field, CALMET also estimates the boundary 

layer parameters used to characterize diffusion and deposition by the dispersion model. 

 

11 http://www.nature.nps.gov/air/maps/Receptors/index.cfm 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-25 

Selected hours of the three-year CALMET/MM5 three-dimensional data set were examined by 

extracting data from the CALMET output files and plotting the meteorological fields with the 

CALDESK software package. Wind vector plots were examined for different times of year, 

different times of day, and for all 10 vertical levels. 

6.4.9 AQRV Calculation Procedures 

The CALPUFF modeling system was used to predict criteria pollutant concentrations, total 

deposition fluxes, and light extinction coefficients attributable to project emissions in regional 

Class I areas. These parameters were calculated from CALPUFF output files using the postprocessor programs CALPOST and POSTUTIL. 

Predictions of NO2 and PM2.5 concentrations in the Class I areas of interest were extracted from 

the annual and short-term emission cases using the CALPOST post-processor. Total nitrogen 

deposition fluxes are calculated by summing and converting the various species included in the 

wet and dry deposition CALPUFF output files. The nitrogen deposition fluxes include the 

nitrogen from the background ammonia to some extent. For comparison to FLM deposition 

criteria, the fluxes were converted to kilograms per hectare per year. 

6.4.10 FLAG 2010 (CALPOST Method 8) 

In order to provide further information, extinction coefficients were calculated using the 

2010revisions to the FLM FLAG procedures. The revised procedures employ the IMPROVE 

extinction equation to calculate bext (invoked with MVISCHECK=1 in CALPOST). This updated 

equation for extinction uses monthly relatively humidity adjustment factors with relative humidity 

capped at 95%. It uses annual background aerosol concentrations recommended by the FLMs 

for the Class I area of concern, and assesses the visibility using the 98th percentile modeled 

values at each receptor. In order to use Method 8, CALPOST Version 6.221 (Level 080724) 

was used to post-process the CALPUFF output files. 

For FLAG 2010, a Project’s extinction is calculated using the revised IMPROVE reconstructed 

mass extinction equation as follows: 

bproject = 2.2 × fS(RH) × [Small Sulfate] + 4.8 × fL(RH) × [Large Sulfate] 

+ 2.4 × fS(RH) × [Small Nitrate] + 5.1 × fL(RH) × [Large Nitrate] 

+ 2.8 × [Small Organic Mass] + 6.1 × [Large Organic Mass] 

+ 10 × [Elemental Carbon] 

+ 1 × [Fine Soil] 

+ 0.6 × [Coarse Mass] 

+ 1.7 × fSS(RH) × [Sea Salt] 

+ Rayleigh Scattering (Site Specific) 

+ 0.33 × [NO2 (ppb)] {or as: 0.1755 × [NO2 (μg/m3)]} 

Where: 

[ ] indicates concentrations in μg/m3 

fS(RH) = Relative humidity adjustment factor for small sulfate and nitrate 

fL(RH) = Relative humidity adjustment factor for large sulfate and nitrate 

fSS(RH) = Relative humidity adjustment factor for sea salt 

For Total Sulfate < 20 μg/m3: 

[Large Sulfate] = ([Total Sulfate] / 20 μg/m3) × [Total Sulfate] 

For Total Sulfate ≥ 20 μg/m3: 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-26 

[Large Sulfate] = [Total Sulfate] 

And: 

[Small Sulfate] = [Total Sulfate] – [Large Sulfate] 

To calculate large and small nitrate and organic mass, substitute ({Large, Small, Total} 

{Nitrate, Organic Mass}) for Sulfate. 

6.4.11 Analysis Results 

The CALPUFF modeling system was used to predict concentrations of NO2 and PM2.5 in the 

Class I area of interest. Table 6.4.11-1 summarizes the predicted maximum NO2 and PM2.5

concentrations and compares them to the Class I SILs. At this point, there are two sets of Class 

I SILs: those proposed by EPA, and those recommended by the FLMs. These proposed and 

recommended SILs were obtained from the Federal Register, Vol. 61, No. 143, p. 38292, July 

23, 1996. As shown in Table 6.4.11-1, the CALPUFF simulations indicate neither the SILs nor 

the increments will be exceeded. 

Table 6.4.11-1 

Maximum Predicted Class I Concentrations 

Criteria Pollutant Averaging Period 

Developer 

Max. 

Concentration 

(μg/m3)

Discoverer 

Americas 

 Max. 

Concentration

(μg/m3)

EPA SIL 

(μg/m3) 

FLM SIL

 (μg/m3) 

NO2 a Annual 0.02 0.02 0.1 0.03 

PM2.5 b 24-hr 0.04 0.04 0.07 -- 

Annual 0.0004 0.0004 0.06 c -- 

Notes: 

a

 NOX was conservatively assumed to be 75 percent converted to NO2.

b 100th percentile (maximum) values are presented (not 98th percentile) using direct PM2.5 emissions only.

c

 The Class I PM2.5 SIL was vacated on January 22, 2013,but presented here for comparison. 

CALPUFF was also used to predict the impacts of acid-forming compounds emitted by the 

project on soils and vegetation in the Class I area of interest. The deposition analysis results 

are shown in Table 6.4.11-2. The National Park Service (NPS) has established Deposition 

Analysis Threshold (DAT) for nitrogen of 0.010 kg/ha/yr for Class I areas to the east of the 

Mississippi river.12 These “thresholds” are based on natural background deposition estimates 

culled from various research efforts, a variability factor, and a safety factor that accounts for 

cumulative effects. The DATs are not adverse impact thresholds, but are intended as 

conservative screening criteria that allow the FLMs to identify potential deposition fluxes that 

require their consideration on a case-by-case basis. As shown in Table 6.4.11-2, predicted 

maximum nitrogen deposition fluxes do not exceed the DATs. 

Table 6.4.11-2

Predicted Class I Area Deposition Fluxes 

 

12 Guidance on Nitrogen and Sulfur Deposition Analysis Thresholds, available on the FLAG internet site at 

http://www2.nature.nps.gov/ard/flagfree/NSDATGuidance.htm 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-27 

 Developer Discoverer Americas 

Class I Area of Interest Nitrogen Deposition Nitrogen Deposition 

Breton Wilderness 0.0013 0.0014 

NPS DAT 0.010 0.010 

Comparison with FLM-recommended criteria for regional visibility impacts is shown by 

calculating the change in 24-hour extinction for each Class I receptor. The FLMs recommend in 

the FLAG Phase I Report that a five percent change in extinction be used to indicate a “just 

perceptible” change to a landscape. The CALPUFF modeling system was used to predict both 

the extinction coefficient attributable to emissions from the project as well as the background 

extinction coefficients for that day’s meteorology. As is required, all days with more than five 

percent change in extinction are disclosed. As shown in Tables 6.4.11-3 and 6.4.11-4, and 

summarized in Table 6.4.11-5, the 98th percentile predicted change in extinction at Breton 

Wilderness using Method 8 was less than 5 percent for two of the three years, for both the 

Developer and the Discoverer Americas emissions scenario. These results are less than the 

ten percent threshold established by the FLMs, which would cause the FLMs to be likely to 

object to the issuance of the permit. The FLMs should take into consideration the conservative 

nature of the modeling, and the relatively low extinction values for the single year that exceeds 

five percent. Conservative assumptions include: 

 24-hour average emission rates were assumed to equal 1-hour maximum emission rates 

 1-hour maximum emission rates were taken from the worst-case possible hour, with all 

equipment operating at 100% load, even emission units that in reality operate just a few 

hours per month. 

 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-28 

Table 6.4.11-3 

Predicted Extinction Change for Breton Wilderness, Method 8, Maersk 

Date 

bexta (1/Mm) Change bext by Componentc (1/Mm) 

Project Bckgrndb Total (%) SO4 NO3 OC EC PMC PMF NO2

12/08/01 3.625 23.365 26.99 15.51 0.009 3.369 0.019 0.182 0 0 0.046 

02/28/01 2.276 23.114 25.39 9.85 0.006 2.107 0.01 0.101 0 0 0.052 

02/19/03 2.266 23.114 25.38 9.8 0.006 2.058 0.014 0.139 0 0 0.048 

11/22/03 2.065 23.235 25.3 8.89 0.008 1.844 0.018 0.176 0 0 0.019 

02/27/01 1.808 23.114 24.922 7.82 0.004 1.715 0.007 0.071 0 0 0.011 

03/16/03 1.702 23.085 24.787 7.37 0.003 1.612 0.007 0.068 0 0 0.012 

02/21/01 1.679 23.114 24.793 7.26 0.003 1.539 0.007 0.072 0 0 0.057 

05/01/03 1.636 23.246 24.882 7.04 0.006 1.499 0.011 0.11 0 0 0.01 

04/05/01 1.61 23.042 24.651 6.99 0.006 1.357 0.015 0.146 0 0 0.086 

02/20/01 1.498 23.114 24.613 6.48 0.004 1.35 0.009 0.09 0 0 0.046 

11/20/02 1.482 23.235 24.717 6.38 0.002 1.401 0.005 0.048 0 0 0.026 

01/28/02 1.418 23.376 24.794 6.07 0.004 1.287 0.009 0.083 0 0 0.035 

02/20/03 1.341 23.114 24.455 5.8 0.003 1.208 0.008 0.073 0 0 0.048 

12/07/01 1.324 23.365 24.689 5.67 0.003 1.223 0.007 0.066 0 0 0.024 

09/17/01 1.176 23.493 24.67 5.01 0.011 0.932 0.021 0.204 0 0 0.009 

Notes:

a

 Project and background extinction values for daily period that resulted in the maximum percent change in extinction. 

b

 Background extinction derived from default annual average extinction components provided in FLAG 2010 Tables. 

c

 Extinction coefficient components are: SO4 = fine sulfate, NO3 = fine nitrate, OC = fine organic carbon, EC = fine elemental carbon, 

PMC = coarse mass, PMF = fine crustal mass, NO2 = nitrogen dioxide. 

 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-29 

Table 6.4.11-4 

Predicted Extinction Change for Breton Wilderness, Method 8, Transocean 

Date 

bexta (1/Mm) Change bext by Componentc (1/Mm) 

Project Bckgrndb Total (%) SO4 NO3 OC EC PMC PMF NO2

12/08/01 5.112 23.365 28.477 21.88 0.011 4.799 0.022 0.216 0 0 0.064 

02/28/01 3.254 23.114 26.368 14.08 0.007 3.04 0.013 0.122 0 0 0.073 

02/19/03 3.194 23.114 26.308 13.82 0.008 2.938 0.017 0.165 0 0 0.067 

11/22/03 2.999 23.235 26.234 12.91 0.01 2.734 0.021 0.209 0 0 0.025 

02/27/01 2.621 23.114 25.735 11.34 0.005 2.507 0.009 0.085 0 0 0.016 

03/16/03 2.474 23.085 25.559 10.72 0.004 2.366 0.008 0.079 0 0 0.017 

02/21/01 2.39 23.114 25.504 10.34 0.004 2.209 0.009 0.086 0 0 0.083 

05/01/03 2.331 23.246 25.577 10.03 0.007 2.167 0.013 0.13 0 0 0.014 

04/05/01 2.299 23.042 25.34 9.98 0.007 1.975 0.018 0.175 0 0 0.123 

02/20/01 2.193 23.114 25.307 9.49 0.005 2.004 0.011 0.107 0 0 0.066 

11/20/02 2.125 23.235 25.36 9.15 0.003 2.025 0.006 0.056 0 0 0.035 

01/28/02 2.049 23.376 25.426 8.77 0.005 1.882 0.01 0.1 0 0 0.052 

02/20/03 1.993 23.114 25.107 8.62 0.004 1.819 0.009 0.09 0 0 0.071 

12/07/01 1.843 23.365 25.208 7.89 0.004 1.719 0.008 0.078 0 0 0.034 

09/17/01 1.689 23.493 25.182 7.19 0.013 1.395 0.025 0.244 0 0 0.013 

04/13/02 1.599 23.042 24.64 6.94 0.002 1.552 0.004 0.035 0 0 0.006 

01/29/02 1.445 23.376 24.822 6.18 0.005 1.231 0.01 0.102 0 0 0.097 

05/26/02 1.424 23.246 24.67 6.13 0.004 1.32 0.008 0.081 0 0 0.011 

07/08/03 1.384 23.733 25.117 5.83 0.008 1.123 0.016 0.157 0 0 0.08 

01/17/02 1.354 23.376 24.731 5.79 0.003 1.28 0.006 0.061 0 0 0.004 

11/26/03 1.277 23.235 24.513 5.5 0.004 1.127 0.01 0.102 0 0 0.033 

02/25/02 1.267 23.114 24.381 5.48 0.003 1.152 0.008 0.075 0 0 0.028 

03/11/01 1.251 23.085 24.336 5.42 0.002 1.149 0.006 0.058 0 0 0.036 

04/24/01 1.229 23.042 24.271 5.33 0.003 1.086 0.008 0.077 0 0 0.055 

05/02/03 1.179 23.246 24.424 5.07 0.003 1.101 0.006 0.057 0 0 0.011 

09/30/02 1.189 23.493 24.682 5.06 0.006 1.042 0.012 0.116 0 0 0.014 

10/09/02 1.162 23.221 24.383 5 0.007 0.919 0.015 0.149 0 0 0.072 

Notes:

a

 Project and background extinction values for daily period that resulted in the maximum percent change in extinction.

b

 Background extinction derived from default annual average extinction components provided in FLAG 2010 Tables.

c

 Extinction coefficient components are: SO4 = fine sulfate, NO3 = fine nitrate, OC = fine organic carbon, EC = fine elemental 

carbon, PMC = coarse mass, PMF = fine crustal mass, NO2 = nitrogen dioxide. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-30 

Table 6.4.11-5 

Maximum Predicted Extinction Change for Breton Wilderness, Method 

8 Summary 

Criteria Developer Discoverer Americas 

Highest Value 15.51 21.88 

Number Days > 5% change 15 27 

Number Days > 10% change 1 8 

98th Percentile Change, 2001 5.01 7.19 

98th Percentile Change, 2002 3.51 5.06 

98th Percentile Change, 2003 3.69 5.07 

6.5 Additional Impacts Assessment 

An additional impacts analysis was performed in accordance with PSD requirements (40 CFR 

52.21(o)). The analysis evaluates the potential impacts that the proposed Statoil exploration 

activities could have on growth, soils, vegetation, and visibility in the area surrounding the 

proposed drilling locations. 

6.5.1 Growth Analysis 

Statoil examined the potential growth in industrial, commercial and residential sources as a 

result of the proposed DeSoto Canyon and Lloyd Ridge drilling exploration activities and 

determined that no growth is expected. This determination was reached based on Statoil’s 

deep understanding of the robust and well developed oil and gas industry that currently 

supports exploration activities in the area just west of the proposed drilling activities. It is 

expected that the current infrastructure is more than adequate to support the proposed drilling 

activities and thus no growth is expected. 

6.5.2 Soil and Vegetation Impacts 

The PSD draft guidelines prescribe that the potential impacts of the proposed project on the 

soils and vegetation in the vicinity of the facility should be considered. As approved in the 

modeling protocol, due to the location of the proposed exploration activities in the eastern Gulf 

of Mexico, no impact to local soils or vegetation is expected. 

6.5.3 Local Visibility Impairment 

Local visibility analysis was conducted using the EPA plume impact screening model 

(VISCREEN, version 1.01). VISCREEN calculates the potential visual impact of a plume of 

specified emissions for specific transport and dispersion conditions. A VISCREEN Level I 

analysis was conducted to estimate if the proposed exploration activities could result in an 

adverse impact on visibility for the closest Class II area receptor. The closest Class II area 

receptor to the lease block in the Gulf of Mexico was located on the edge of the Mississippi 

Delta, over 50km away. To maintain a conservative analysis, and because VISCREEN is not 

applicable beyond 50km, 50km was used as the source to class I area distance. Level I 

analysis utilizes particulate matter and NOx emission rates as inputs, while using default values 

for background ozone, stability class and wind speed. The default background ozone 

concentration is 0.04 ppm, while default stability and wind speed are 6 and 1 m/s, respectively. 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-31 

The model conservatively evaluates whether a plume from Developer or Discoverer Americas 

drilling vessels and associated support vessels is perceptible to an observer under worst case 

meteorological conditions from a known distance. Several angles between the observer’s line 

of sight and the sun’s radiation (θ) are considered. The input emission rates for Developer or 

Discoverer Americas drilling vessels and associated support vessels are listed in Tables 6.5.3-1 

and 6.5.3-2. The default input parameters are listed in Table 6.5.3-3. 

Table 6.5.3-1 

Level I Developer VISCREEN Analysis Input Parameters 

Developer Short-Term Emission Rates Emissions (lb/hr) 

Particulate Matter 13.82 

NOx (as NO2) 579.32 

Primary NO2 0 (default) 

Soot 0 (default) 

Primary SO4 0 (default) 

Table 6.5.3-2 

Level I Discoverer Americas VISCREEN Analysis Input Parameters 

Discoverer Americas Short-Term Emission Rates Emissions (lb/hr) 

Particulate Matter 16.55 

NOx (as NO2) 818.68 

Primary NO2 0 (default) 

Soot 0 (default) 

Primary SO4 0 (default) 

Table 6.5.3-3 

Level I Developer and Discoverer Americas VISCREEN Analysis Input Parameters 

Input Parameters 

Background Ozone (ppm) 0.04 

Background Visual Range (km) 20 

Distance: Source to Closest Class I Area (km) 50 

Distance: Source to Farthest Class I Area (km) 50 

Source-Observer Distance (km) 50 

Plume-Source-Observer Angle 11.25 

Stability 6.0 

Wind Speed (m/s) 1.0 

The VISCREEN model is designed to determine whether the plume from an emission source 

has the potential to be traceable to an untrained observer under reasonable worst case 

conditions. Two screening criteria are used to carry out the analysis and if either criterion is 

exceeded, more comprehensive analyses should be carried out. The first criterion, delta E, 

known as the plume perceptibility parameter is based on the difference in color and brightness 
Outer Continental Shelf PSD/Title V Permit Application 

Air Quality Impact Assessment 6-32 

between the plume and the background. It is also known as the color difference parameter and 

depends on three factors, namely, brightness (L), color hue (a) and color saturation (b). 

Mathematically, 

 ΔE = [(ΔL)2

 + (Δa)2 + (Δb)2]

1/2 

The default threshold for delta E is 2.0 

The second criterion is called the green contrast value (Cplume or Cp). Cp is defined as the contrast 

of a plume against a viewing background such as the sky or a terrain feature. Change is 

measured in terms of green color (wavelength=0.55 microns). The default threshold for Cp is 

0.05. Level I screening results are listed in Table 6.5.3-4 and Table 6.5.3-5. 

Table 6.5.3-4 

Level I Developer VISCREEN Results 

Background θ 

Distance 

(Source-Observer) (km) 

Delta E Contrast 

Critical Plume Critical Plume 

Sky 10 50 2.00 1.088 0.05 -0.006 

Sky 140 50 2.00 0.337 0.05 -0.007 

Terrain 10 50 2.00 0.087 0.05 0.001 

Terrain 140 50 2.00 0.026 0.05 0.001 

Table 6.5.3-5 

Level I Discoverer Americas VISCREEN Results 

Background θ 

Distance 

(Source-Observer) (km) 

Delta E Contrast 

Critical Plume Critical Plume 

Sky 10 50 2.00 1.449 0.05 -0.008 

Sky 140 50 2.00 0.449 0.05 -0.010 

Terrain 10 50 2.00 0.118 0.05 0.002 

Terrain 140 50 2.00 0.036 0.05 0.002 

As listed in Table 6.5.3-4 and Table 6.5.3-5 above the default threshold for delta E and Cp was 

not exceeded for both sky and terrain backgrounds for either Developer or Discoverer Americas; 

therefore, the proposed exploration activities are not expected to impair the local visibility. 

VISCREEN modeling outputs are included with this air quality impact analysis. 

6.5.4 Ozone Assessment 

As documented in the analysis below, Statoil has concluded that the proposed exploratory 

drilling activities will not significantly impact the current ozone levels in the eastern Gulf of 

Mexico. This conclusion is based on the relatively low quantity of project emissions, the 

distance needed to travel to impact ground-level ozone and the frequent wind direction 

changes. 
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Air Quality Impact Assessment 6-33 

6.5.4.1 Ozone Formation 

Ozone is an air pollutant formed through complex chemical reactions of nitrogen oxide (NOx) 

and volatile organic compound (VOC) emissions, during periods of conducive weather 

conditions. Ozone is more readily formed when it is sunny and hot and the air is stagnant. 

Conversely, ozone production is more limited when it is cloudy, cool, rainy, and windy. For 

these reasons, ozone concentrations are generally the highest during the summer. 

The majority of tropospheric ozone formation occurs when nitrogen oxides (NOx), carbon 

monoxide (CO) and volatile organic compounds (VOCs) react in the atmosphere in the 

presence of sunlight. NOx, CO, and VOCs are called ozone precursors. The chemical 

reactions involved in tropospheric ozone formation are a series of complex cycles in which 

carbon monoxide and VOCs are oxidized to water vapor and carbon dioxide. The reactions 

involved in this process are illustrated below with CO but similar reactions occur for VOC as 

well. Oxidation begins with the reaction of CO with the hydroxyl radical. The hydrogen atom 

formed by this reacts rapidly with oxygen to give a peroxy radical HO2

OH + CO → H + CO2

H + O2 → HO2

Peroxy radicals then go on to react with NO to give NO2, which is photolysed (indicated by hν) 

to give atomic oxygen and through reaction with oxygen a molecule of ozone: 

HO2 + NO → OH + NO2

NO2 + hν → NO + O 

O + O2 → O3

The net effect of these reactions is: 

CO + 2O2 → CO2 + O3

This cycle involving HOx and NOx is terminated by the reaction of OH with NO2 to form nitric 

acid or by the reaction of peroxy radicals with each other to form peroxides. The chemistry 

involving VOCs is much more complex but the same reaction of peroxy radicals oxidizing NO to 

NO2 is the critical step leading to ozone formation. 

6.5.4.2 Project Emissions Relative to Existing Emissions 

For this project, the estimated annual emissions for NOx and VOCs are shown in Table 6.5.4.2-

1, for the Maersk Developer and Transocean Discoverer Americas. The estimated emissions 

include the contributions from the support fleet, including crew boats, and supply vessels. 

Because the sum of NOx emissions exceeds 100 tons per year, an assessment of the project’s 

potential effects on regional ozone concentrations is required. 

According to the information presented in the Oil and Gas Exploration section on the NOAA 

Ocean Explorer website13 there are 3,858 oil rigs or platforms in the Western and Central 

Planning Areas of the Gulf of Mexico (GOM). The locations of these oil rigs and platforms are 

 

13 http://oceanexplorer.noaa.gov/explorations/06mexico/background/oil/oil.html
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Air Quality Impact Assessment 6-34 

shown in Figure 4. Figure 4 also illustrates the Statoil lease block locations in relation to the 

current oil and gas well locations in the GOM. 
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Air Quality Impact Assessment 6-35 
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Air Quality Impact Assessment 6-36 

Further analysis based on the 2008 Emissions Inventory from the Bureau of Safety and 

Environmental Enforcement (BSEE) showed that some of these rigs or platforms are either 

inactive, weren’t included in the emissions inventory report, or have been decommissioned. In 

2008 there were 3,027 point sources emitted either VOC or NOx and were located west of the 

87 degree 30 minute Longitude. 

The emissions data found in the BOEMRE 2008 Gulfwide Emission Inventory Study Report14

(the latest finalized inventory) is summarized in Table 6.5.4.2-1, for comparison with Statoil’s 

estimated potential annual emissions. 

Table 6.5.4.2-1 

2008 Emissions of NOx and VOCs from Point Sources in the Gulf of Mexico 

Pollutant Source Emissions (TPY) 

NOX Maersk Developer 484 

VOC Maersk Developer 28 

NOX Transocean Discoverer Americas 560 

VOC Transocean Discoverer Americas 25 

NOX 1,388 Existing Emission Points 74,286 

VOC 3,026 Existing Emission Points 60,824 

When compared with the total emission amounts for NOx and VOCs from all the sources in Gulf 

of Mexico, the proposed project emissions will at most account for 0.8% of total NOx and 0.05% 

of total VOC emissions, respectively. 

Table 6.5.4.2-2 presents the statewide total NOx emissions from the 2008 National Emissions 

Inventory (NEI)15 for the States around the Gulf of Mexico. The total NOx emissions for these 

States are summarized based on the information in the Technical Support Document (TSD) for 

the EPA Federal Transportation Rule (TR) (EPA-HQ-OAR-2009-0491). The TSD also showed 

that the on-road sources contributed 36% to the total NOx emissions in the Gulf States. 

Estimated project emissions are very small compared with the total NOx emissions of nearly 4.0 

million tons from the five states in the region. 

 

14 http://www.bsee.gov/Environmental-Stewardship/Environmental-Studies/Gulf-of-Mexico-Region/AirQuality/2008-Gulfwide-Emission-Inventory.aspx

15 http://www.epa.gov/ttnchie1/net/2008inventory.html
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Air Quality Impact Assessment 6-37 

Table 6.5.4.2-2 

State - Level Total NOx Emissions for Gulf States in the 2008 NEI 

State NOx Emissions (TPY) 

Alabama 421,467 

Florida 895,436 

Louisiana 548,439 

Mississippi 278,745 

Texas 1,827,200 

Total 3,971,287 

Ozone concentrations measured at the sites shown in Figure 5 are much more likely to be the 

result of the vast quantity of NOx and VOC emissions from existing mobile (traffic) and onshore 

point (e.g. refineries) sources, rather than from the much smaller emissions associated with the 

project. 

Figure 5. Ozone Monitors closest to the Statoil Lease Blocks 

In addition, the Statoil lease block closest to shore is more than 150 km (93 miles) from the 

nearest coastline at the mouth of the Mississippi Delta. As such, the project’s NOx and VOC 

emissions will need to travel more than 100 miles to reach the coastline to contribute to onshore ozone concentrations. Furthermore, as shown in Figure 6, the wind speed and direction 
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Air Quality Impact Assessment 6-38 

in the EGOM frequently changes; as such, the emissions from this project will be dispersed over 

a wide area. 

Figure 6 Wind Rose of EGOM Weather Buoy (WMO #995000) 16

 

16 WRPLOT View – Lakes Environmental Software 
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Air Quality Impact Assessment 6-39 

Based on the above analysis and with the consideration of: 

 The total number of oil rigs and platforms in the Western Gulf of Mexico and the total 

emissions of NOx and VOCs from these existing sources; 

 The distance between the Statoil lease blocks and the nearest coastline; 

 Total NOx emissions from the States around the Gulf of Mexico; and, 

 Frequent wind direction change and atmospheric disturbances in the Gulf of Mexico; 

We do not expect project emissions to impact ozone formation on the coastal areas around the 

Gulf of Mexico.