Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-1 ENVIRON

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, which was subsequently approved by 

FWS on July 30, 2012. ENVIRON discussed the protocol with Stan Krivo of EPA Region IV on 

August 28, 2012 and no deficiencies were mentioned. A copy of the approved protocol is

provided in Appendix E (Attachment 1) of this application. ENVIRON followed the approved 

protocol in performing this air quality impact assessment. Please find attached an electronic 

copy of all modeling files associated with this analysis in Appendix E (Attachment 2). 

As documented in Section 4.1 of this document 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. ENVIRON applied computer-based dispersion 

modeling techniques to simulate dispersion of emissions attributable to the proposed 

exploration activities. The results of the modeling are 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, because of its design for long-range transport applications beyond 50 km. The 

modeling domain is shown in Figure 4 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 more than 200 km from the source, 

building downwash effects will not significantly affect the results and have been ignored. 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-2 ENVIRON

100 km

200 km

300 km

Full Vistas Domain

Closest Lease Block

Statoil OCS CALPUFF Domain

Brigantine Wilderness

Chassahowitzka Wilderness

Saint Marks Wilderness

Breton Wilderness

700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800

LCC (RPO Projection) Easting, km

-1600

-1500

-1400

-1300

-1200

-1100

-1000

-900

-800 CC o t g, 

Figure 4. CALPUFF modeling domain (blue box), with “25 mile” receptors (red)
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-3 ENVIRON

6.2 Model Application

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

FWS.

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)

• Support Vessels (e.g. crew boats)

Discoverer Americas emission sources include the following:

• Main Generator Engines (6)

• Emergency Generator Engine (1)

• Life Boats (6)

• Rescue Boat (1)

• Hot Oil Heater (1)1

• Emergency Air Compressor Engines (2)

• Support Vessels (e.g. crew boats)

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

are discussed in Section 6.2.4 below. 

 1 The cargo heater is used only twice per year for one hour each time, or only one hour of operation per 180-day drilling campaign.

It therefore cannot contribute to the Class II 1-hour NO2, 24-hour PM2.5 values, or the Class I Visibility value (all 98th percentile 

days) nor the Class I PM2.5 Increment (second high day). Its contribution to annual average emissions is very small, several orders 

of magnitude smaller than any other emission unit. The cargo heater was therefore not included in the modeling scenario.
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-4 ENVIRON

6.2.2 Modeling Scenario

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

Discoverer Americas drilling units to conduct exploratory drilling in the OCS of the Eastern Gulf 

of Mexico. As outlined in this application, Statoil will only use one drilling vessel at any given 

time; therefore, the modeling analysis only addresses one vessel operating at any time. 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. Statoil evaluated the various potential operating 

scenarios to determine which emissions and release parameters would result in maximum 

impact at the modeled receptors. Because of the distance between the closest receptors and 

the emissions sources, Statoil determined 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. It is 

possible that these sources could operate at less than the maximum proposed load conditions. 

However, any changes in stack parameters resulting from the lower loads would not result in 

higher impacts at the modeled receptors. Ultimately, Statoil determined that worst-case impacts 

would be represented by the operating scenario described in this section.

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 applicable 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 at 100% load and

hourly emissions for support vessels (Crew Boats and Supply Boats) are derived from the 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-5 ENVIRON

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 the adjusted fuel usage or 

adjusted power rating (depending on the vessel type) for the proposed annual run time.

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

engines operating at 80% load. Auxiliary equipment (i.e., emergency generator engine, 

emergency air compressor 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. Annual emissions also include all 

auxiliary equipment at 100% load and support vessels based on the adjusted fuel usage for the 

proposed annual run time. 

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. Statoil has included both a crew 

boat and an OSV in the short-term modeling scenario. 

Statoil modeled the support vessels for each drilling vessel as a series of volume sources 

placed along a line originating at the drilling vessel and extending out 25 miles in the direction of 

the Breton Wilderness. In reality, crew boats and offshore support vessels will likely take a 

different course than this, and may in fact take a different course when arriving at the drilling 

vessel than when departing from it. Modeling both support vessels’ emissions as a series of 

volume sources, with the worst-case course (directly toward the Breton Wilderness) is 

conservative for the maximum 24-hour impact.2

 

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 volume sources placed evenly along the line. Statoil chose 

to use 10 volume sources, because 25 miles is approximately 40 km and the CALMET grid (see 

Section 6.2.7) uses a 4 km grid spacing. 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. 

 2 Approach discussed and approved during phone conversation with Mr. Stan Krivo on March 2, 2010. 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-6 ENVIRON

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

scenario are 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 shoreline and Class I 

receptors and 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 

shoreline 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 and Crew vessels present, at 100% load

 Maximum annual emission rates:

• 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

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

and emergency air compressors) at 100% load

• OSV and Crew vessels present, at 100% load

 Maximum annual emission rates:

• Three Main Generator engines at 35% load

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

and emergency air compressors) at 100% load

• OSV and Crew vessels present, based on maximum annual operation

6.2.3 Stack Parameters

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 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-7 ENVIRON

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

in the dispersion modeling simulations. 

For stacks with a vertical discharge, Statoil used available stack parameter data (i.e., stack 

diameter, stack exit velocity, and stack exit temperature). For stacks with horizontal or angled 

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

but maintain thermal plume rise, by using a stack exit velocity of 0.001 meters per second (m/s). 

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. Stack parameters for emission sources 

modeled as volume sources are listed in Table 6.2.3-3.

Table 6.2.3-1

Developer Point Source Stack Parameters

Used in CALPUFF Modeling Analysis

Stack

Modeling 

ID

X-Coord 

(LCC)

Y-Coord

(LCC)

Height

(m)

Elevation 

(m)

Diameter 

(m)

Exit 

Velocity 

(m/s)

Exit Temp 

(K)

Wartsila Diesel 

Generator Engine 1 GEN1 941.931 -1186.229 28.93 0 0.81 0.001 623.15

Wartsila Diesel

Generator Engine 2 GEN2 941.931 -1186.228 28.93 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 3 GEN3 941.931 -1186.229 26.82 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 4 GEN4 941.931 -1186.228 26.82 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 5 GEN5 941.931 -1186.300 28.93 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 6 GEN6 941.931 -1186.302 28.93 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 7 GEN7 941.931 -1186.300 26.82 0 0.81 0.001 623.15

Wartsila Diesel 

Generator Engine 8 GEN8 941.931 -1186.302 26.82 0 0.81 0.001 623.15

Emergency Diesel 

Generator Engine EGEN1 942.005 -1186.225 9.45 0 0.41 0.001 888.15

Lifeboat 1 LB1 942.024 -1186.260 19.70 0 0.89 0.001 830.15

Lifeboat 2 LB2 942.024 -1186.270 19.70 0 0.89 0.001 830.15

Lifeboat 3 LB3 941.939 -1186.256 19.70 0 0.89 0.001 830.15

Lifeboat 4 LB4 941.939 -1186.267 19.70 0 0.89 0.001 830.15

Fast Rescue Boat 

Engine #1 MOB1 941.927 -1186.264 19.70 0 1.85 0.001 773.15

Cement Unit 

Engine (CMU-1) CMU1 941.979 -1186.304 9.45 0 0.20 0.001 794.15

Cement Unit 

Engine (CMU-2) CMU2 941.981 -1186.304 9.45 0 0.20 0.001 794.15
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-8 ENVIRON

Table 6.2.3-2

Discoverer Americas Point Source Stack Parameters 

Used in CALPUFF Modeling Analysis

Stack

Modeling 

ID

X-Coord 

(LCC)

Y-Coord

(LCC)

Height

(m)

Elevation 

(m) Diameter (m)

Exit 

Velocity 

(m/s)

Exit 

Temp 

(K)

Gen. Engine 1 GEN1 941.853 -1186.259 21.33 0 1.00 16.49 640.00

Gen. Engine 2 GEN2 941.852 -1186.261 21.33 0 1.00 16.49 640.00

Gen. Engine 3 GEN3 941.853 -1186.262 21.33 0 1.00 16.49 640.00

Gen. Engine 4 GEN4 941.853 -1186.268 21.33 0 1.00 16.49 640.00

Gen. Engine 5 GEN5 941.852 -1186.269 21.33 0 1.00 16.49 640.00

Gen. Engine 6 GEN6 941.853 -1186.271 21.33 0 1.00 16.49 640.00

E-Gen. Engine EGEN 942.063 -1186.250 21.33 0 0.60 14.12 640.00

Lifeboat 1 LB1 942.072 -1186.283 12.74 0 0.05 0.001 830.15

Lifeboat 2 LB2 942.072 -1186.247 12.74 0 0.05 0.001 830.15

Lifeboat 3 LB3 942.061 -1186.283 12.74 0 0.05 0.001 830.15

Lifeboat 4 LB4 942.061 -1186.247 12.74 0 0.05 0.001 830.15

Lifeboat 5 LB5 941.843 -1186.282 12.74 0 0.05 0.001 830.15

Lifeboat 6 LB6 941.843 -1186.248 12.74 0 0.05 0.001 830.15

MOB Engine 1 MOB 942.050 -1186.285 12.74 0 0.11 0.001 830.15

Air Compressor 1 ACOMP1 941.843 -1186.282 15.85 0 0.04 0.001 773.00

Air Compressor 2 ACOMP2 941.843 -1186.282 1.83 0 0.04 0.001 773.00
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-9 ENVIRON

The volume sources used 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). The height of the 

release was based on SCREEN3 runs performed following the precedents of the Shell Chuckchi 

Sea permitting effort and the Shell EGOM permitting effort. Actual stack parameters, along with 

ship body dimensions (as building height) were input, along with stability class 4 and a wind 

speed of 20 m/s. The resulting plume rise is conservatively low. The σy was set to the centerto-center distance between adjacent volume sources, divided by 2.15. The σz was taken to be 

the average height of the offshore support vessels, divided by 2.15.

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

summarized in Tables 6.2.3-4 through 6.2.3-13. 

Table 6.2.3-3

Volume Source Stack Parameters for Support Vessels

Used in CALPUFF Modeling Analysis

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

VOL01 901.865 -1163.096 19.41 0 2393 13.7

VOL02 906.319 -1165.671 19.41 0 2393 13.7

VOL03 910.773 -1168.245 19.41 0 2393 13.7

VOL04 915.228 -1170.820 19.41 0 2393 13.7

VOL05 919.682 -1173.394 19.41 0 2393 13.7

VOL06 924.136 -1175.969 19.41 0 2393 13.7

VOL07 928.591 -1178.543 19.41 0 2393 13.7

VOL08 933.045 -1181.118 19.41 0 2393 13.7

VOL09 937.500 -1183.692 19.41 0 2393 13.7

VOL10 941.954 -1186.267 19.41 0 2393 13.7
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-10 ENVIRON

Table 6.2.3-4

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 6.2.3-5

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

(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 3.75E-03 4.86E+00 0 1.94E-04 1.16E-01 3.52E-02 0 0

LB1 3.97E-05 8.62E-05 4.51E-02 0 4.47E-06 2.67E-03 8.09E-04 0 0

LB2 3.97E-05 8.62E-05 4.51E-02 0 4.47E-06 2.67E-03 8.09E-04 0 0

LB3 3.97E-05 8.62E-05 4.51E-02 0 4.47E-06 2.67E-03 8.09E-04 0 0

LB4 3.97E-05 8.62E-05 4.51E-02 0 4.47E-06 2.67E-03 8.09E-04 0 0

MOB1 2.23E-04 3.23E-04 2.53E-01 0 1.67E-05 1.00E-02 3.03E-03 0 0

CMU1 6.85E-04 4.96E-04 7.46E-01 0 2.57E-05 1.54E-02 4.65E-03 0 0

CMU2 6.85E-04 4.96E-04 7.46E-01 0 2.57E-05 1.54E-02 4.65E-03 0 0
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-11 ENVIRON

Table 6.2.3-6

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 6.2.3-7

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

(g/s)

GEN1 2.69E-03 1.46E-03 3.32E+00 0 7.57E-05 4.52E-02 1.37E-02 0 0

GEN2 2.69E-03 1.46E-03 3.32E+00 0 7.57E-05 4.52E-02 1.37E-02 0 0

GEN3 2.69E-03 1.46E-03 3.32E+00 0 7.57E-05 4.52E-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 1.69E-05 2.18E-02 0 8.74E-07 5.22E-04 1.58E-04 0 0

LB1 5.43E-08 1.18E-07 6.16E-05 0 6.11E-09 3.65E-06 1.11E-06 0 0

LB2 5.43E-08 1.18E-07 6.16E-05 0 6.11E-09 3.65E-06 1.11E-06 0 0

LB3 5.43E-08 1.18E-07 6.16E-05 0 6.11E-09 3.65E-06 1.11E-06 0 0

LB4 5.43E-08 1.18E-07 6.16E-05 0 6.11E-09 3.65E-06 1.11E-06 0 0

MOB1 3.05E-07 4.42E-07 3.46E-04 0 2.29E-08 1.37E-05 4.14E-06 0 0

CMU1 4.68E-06 3.39E-06 5.10E-03 0 1.76E-07 1.05E-04 3.18E-05 0 0

CMU2 4.68E-06 3.39E-06 5.10E-03 0 1.76E-07 1.05E-04 3.18E-05 0 0
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-12 ENVIRON

Table 6.2.3-8

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 49.90 0.03 1.21

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 0.62 0.0005 0.03

ACOMP2 0.84 0.0007 0.04

Table 6.2.3-9

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

(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 4.24E-03 3.63E-03 6.29E+00 0 1.88E-04 1.13E-01 3.41E-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 6.85E-05 7.91E-05 7.77E-02 0 4.10E-06 2.45E-03 7.42E-04 0 0

ACOMP2 9.31E-05 1.08E-04 1.06E-01 0 5.57E-06 3.33E-03 1.01E-03 0 0
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-13 ENVIRON

Table 6.2.3-10

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 1.0 0.0007 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 0.000002 0.00008

ACOMP2 0.003 0.000002 0.00011
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-14 ENVIRON

Table 6.2.3-11

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

(g/s)

GEN1 2.21E-03 1.20E-03 4.04E+00 0 6.23E-05 3.72E-02 1.13E-02 0 0

GEN2 2.21E-03 1.20E-03 4.04E+00 0 6.23E-05 3.72E-02 1.13E-02 0 0

GEN3 2.21E-03 1.20E-03 4.04E+00 0 6.23E-05 3.72E-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 2.00E-05 1.71E-05 2.97E-02 0 8.89E-07 5.31E-04 1.61E-04 0 0

LB1 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

LB2 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

LB3 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

LB4 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

LB5 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

LB6 6.74E-08 1.17E-07 7.64E-05 0 6.05E-09 3.62E-06 1.09E-06 0 0

MOB 3.97E-07 4.58E-07 4.50E-04 0 2.37E-08 1.42E-05 4.30E-06 0 0

ACOM

P1 4.68E-08 5.40E-08 5.31E-05 0 2.80E-09 1.67E-06 5.07E-07 0 0

ACOM

P2 6.37E-08 7.35E-08 7.22E-05 0 3.81E-09 2.28E-06 6.89E-07 0 0
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-15 ENVIRON

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 more than 150 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 

(2008). 

Table 6.2.3-12

Short-Term Speciated Emission Rates From Volume Sources Used In Developer and 

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

(g/s)

VOL01 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL02 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL03 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL04 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL05 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL06 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL07 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL08 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL09 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

VOL10 2.44E-03 1.42E-03 2.66E+00 0 7.35E-05 4.39E-02 1.33E-02 0 0

Table 6.2.3-13

Long-Term Speciated Emission Rates From Volume Sources Used In Developer and 

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

(g/s)

VOL01 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL02 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL03 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL04 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL05 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL06 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL07 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL08 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL09 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0

VOL10 3.20E-04 1.86E-04 3.49E-01 0 9.61E-06 5.75E-03 1.74E-03 0 0
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-16 ENVIRON

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 Florida3

. 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 of 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).

Class I receptors for the Breton Wilderness were taken from the NPS website4

, and include 

elevations ranging from 0.021 to 0.375 m. These are the FLM-specified receptors.

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 shoreline 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.

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. 

 3 U. S. Commission on Ocean Policy. Primer on Ocean Jurisdictions: Drawing Lines in the Water. Final Report. 4 http://www.nature.nps.gov/air/maps/Receptors/index.cfm
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-17 ENVIRON

6.3.1 Criteria Pollutant Concentrations

ENVIRON modeled the criteria pollutant concentrations using the emission rates presented 

above in Tables 6.2.3-4 through 6.2.3-7 and Tables 6.2.3-8 through 6.2.3-11 for Developer and 

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

and PM2.5. Tables 6.2.3-12 through 6.2.3-13 presented above list the short-term and annual 

emission rates for modeled volume sources associated with the crew boats and OSV’s used in 

the CALPUFF modeling analysis. 

In order to assess the significance of the predictions, ENVIRON compared the maximum criteria 

pollutant concentrations at the discrete 25-mile receptors predicted by CALPUFF with the Class 

II PSD SIL for NO2 and PM2.5. 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.5 

Similarly, ENVIRON compared the maximum criteria pollutant concentrations at the discrete 

shoreline 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.

The results of the CALPUFF modeling analysis are compared to the SIL and SMC 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 concentrations are less than the applicable SMC; therefore, no monitoring is required.

 5 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 6-18 ENVIRON

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 b 3.4 5.0 7.5 c None c

Annual 0.01 0.01 1.0 14

PM2.5

24-hr b 0.10 0.07 1.2 4

Annual 0.001 0.001 0.3 None

Not

es:

a NOX was assumed to be 100 percent converted to NO2.

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 levels have not yet been 

proposed.

.

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. 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 

the FWS on July 23, 2012, which was subsequently approved on July 30, 2012.

6

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. 

 6 Email correspondence from Jill Webster, dated July 30, 2012.
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-19 ENVIRON

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.

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 (June 2008). 

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 their required 

CALMET setting in a memo issued on August 31, 2009 (Fox 2009).7

 

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 

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

http://www.epa.gov/ttn/scram/CALMET%20CLARIFICATION.pdf
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-20 ENVIRON

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.8

 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 24-hour fuel usage. Maximum shortterm 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, 

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). 

 8 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 6-21 ENVIRON

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 Service. Figure 4 also shows the discrete receptor locations within the 

Breton Class I area.9

 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, nine overwater stations and 

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

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

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

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. 

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.

 9 http://www2.nature.nps.gov/air/Maps/Receptors/index.cfm
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-22 ENVIRON

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 2008 (CALPOST Method 8)

In order to provide further information, extinction coefficients were calculated using the 2008 

proposed revisions 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 2008, 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: 

[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 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-23 ENVIRON

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

23, 1996. As shown in Table 6.4.12-1, 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 0.003 0.003 0.1 0.03

PM2.5 b 24-hr 0.04 0.03 0.07 --

Annual 0.0005 0.0002 0.06 --

Notes:

a NOX was conservatively assumed to be 100 percent converted to NO2.

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

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.10 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

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 

 10 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 6-24 ENVIRON

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. However, most of these days were likely impacted 

by natural obscuration (fog, drizzle, etc.). As shown in Tables 6.4.11-3 and 6.4.11-4, and 

summarized in Table 6.4.12-5, the 98th percentile predicted change in extinction at Breton 

Wilderness using Method 8 was 4.17 percent for the Developer, and 5.14 percent for the 

Discoverer Americas emissions scenario. These results are less than the ten percent threshold 

established by the FLMs, indicating compliance with the criteria.

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 3.539 23.365 26.904 15.15 0.076 3.152 0.025 0.243 0 0 0.044

02/28/01 2.421 23.114 25.535 10.48 0.071 2.134 0.015 0.149 0 0 0.052

02/19/03 2.351 23.114 25.465 10.17 0.047 2.052 0.019 0.19 0 0 0.043

11/22/03 2.104 23.235 25.339 9.06 0.052 1.765 0.025 0.246 0 0 0.015

02/27/01 1.966 23.114 25.08 8.51 0.048 1.791 0.011 0.104 0 0 0.011

02/21/01 1.762 23.114 24.876 7.62 0.028 1.559 0.011 0.105 0 0 0.059

03/16/03 1.748 23.085 24.834 7.57 0.031 1.61 0.009 0.089 0 0 0.01

05/01/03 1.739 23.246 24.985 7.48 0.061 1.494 0.016 0.159 0 0 0.01

04/05/01 1.713 23.042 24.754 7.43 0.036 1.354 0.022 0.215 0 0 0.086

02/20/03 1.667 23.114 24.782 7.21 0.019 1.449 0.013 0.126 0 0 0.061

02/20/01 1.554 23.114 24.668 6.72 0.031 1.342 0.013 0.125 0 0 0.044

12/07/01 1.551 23.365 24.916 6.64 0.028 1.381 0.011 0.102 0 0 0.03

01/28/02 1.547 23.376 24.923 6.62 0.033 1.343 0.012 0.12 0 0 0.038

11/20/02 1.4 23.235 24.635 6.03 0.016 1.295 0.006 0.061 0 0 0.023

09/17/01 1.38 23.493 24.873 5.87 0.086 0.96 0.03 0.293 0 0 0.011

04/13/02 1.199 23.042 24.241 5.21 0.029 1.114 0.005 0.046 0 0 0.005

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 6-25 ENVIRON

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 4.574 23.365 27.938 19.57 0.010 4.295 0.02 0.192 0 0 0.057

02/19/03 2.914 23.114 26.028 12.61 0.007 2.68 0.015 0.15 0 0 0.061

02/28/01 2.774 23.114 25.888 12.00 0.006 2.58 0.011 0.111 0 0 0.065

11/22/03 2.606 23.235 25.841 11.21 0.009 2.364 0.02 0.191 0 0 0.022

02/21/01 2.244 23.114 25.358 9.71 0.004 2.07 0.008 0.083 0 0 0.079

02/27/01 2.231 23.114 25.345 9.65 0.004 2.127 0.008 0.076 0 0 0.016

05/01/03 2.241 23.246 25.487 9.64 0.007 2.075 0.014 0.132 0 0 0.014

02/20/03 2.147 23.114 25.261 9.29 0.004 1.949 0.01 0.102 0 0 0.08

04/05/01 2.115 23.042 25.157 9.18 0.007 1.804 0.017 0.169 0 0 0.116

03/16/03 2.008 23.085 25.093 8.70 0.003 1.91 0.007 0.068 0 0 0.019

02/20/01 1.989 23.114 25.103 8.61 0.005 1.813 0.01 0.1 0 0 0.062

01/28/02 2.011 23.376 25.388 8.60 0.005 1.848 0.01 0.097 0 0 0.051

12/07/01 1.928 23.365 25.293 8.25 0.004 1.792 0.009 0.085 0 0 0.038

11/20/02 1.717 23.235 24.952 7.39 0.002 1.634 0.004 0.044 0 0 0.033

09/17/01 1.636 23.493 25.129 6.96 0.012 1.35 0.024 0.235 0 0 0.014

04/13/02 1.566 23.042 24.608 6.80 0.002 1.516 0.004 0.038 0 0 0.007

01/29/02 1.371 23.376 24.747 5.86 0.005 1.165 0.01 0.098 0 0 0.093

05/26/02 1.358 23.246 24.604 5.84 0.004 1.258 0.008 0.079 0 0 0.01

07/08/03 1.291 23.733 25.024 5.44 0.008 1.036 0.015 0.15 0 0 0.081

11/26/03 1.219 23.235 24.454 5.25 0.004 1.077 0.01 0.095 0 0 0.032

01/17/02 1.214 23.376 24.591 5.19 0.003 1.149 0.006 0.054 0 0 0.003

03/11/01 1.187 23.085 24.272 5.14 0.002 1.093 0.006 0.055 0 0 0.032

10/26/02 1.186 23.221 24.407 5.11 0.002 1.044 0.004 0.04 0 0 0.095

04/24/01 1.158 23.042 24.2 5.03 0.003 1.025 0.007 0.072 0 0 0.05

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.

Table 6.4.11-5

Maximum Predicted Extinction Change for Breton Wilderness, 

Method 8 Summary

Criteria Developer

Discoverer 

Americas

Highest Value 15.15 19.57

Number Days > 5% change 16 24

Number Days > 10% change 3 4

98th Percentile Change, 2001 5.87 6.96

98th Percentile Change, 2002 4.06 4.93

98th Percentile Change, 2003 4.19 4.31

98th Percentile Change over 3 years 4.17 5.14
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-26 ENVIRON

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. 

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. 
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-27 ENVIRON

Table 6.5.3-1

Level I Developer VISCREEN Analysis Input Parameters

Developer Short-Term Emission 

Rates

Emissions 

(lb/hr)

Particulate Matter 15.67

NOx (as NO2) 778.20

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 15.67

NOx (as NO2) 778.20

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 

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
Outer Continental Shelf PSD/Title V Permit Application

Air Quality Impact Assessment 6-28 ENVIRON

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 0.969 0.05 -0.005

Sky 140 50 2.00 0.300 0.05 -0.006

Terrain 10 50 2.00 0.058 0.05 0.001

Terrain 140 50 2.00 0.018 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 1.337 0.05 -0.008

Sky 140 50 2.00 0.415 0.05 -0.009

Terrain 10 50 2.00 0.082 0.05 0.001

Terrain 140 50 2.00 0.025 0.05 0.001

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 in Appendix E (Attachment 3).