### April 24

, 2013

Mr. Stan Krivo

USEPA Region 4

Air Permits Section

61 Forsyth Street SW

Atlanta, GA 30303

- 8960

Re: Statoil Updated Air Quality Analysis

– Remaining Issues

Statoil Gulf Services, LLC

Title V and PSD Permit Application

OCS Drilling and Exploration Activities

Dear Mr. Krivo :

Statoil Gulf Services, LLC (Statoil) submitted a Title V and Prevention of Significant

Deterioration (PSD) permit application for proposed exploratory drilling in the Outer Continental

Shelf (OCS) in the eastern Gulf of Mexico to EPA on September 5 , 2012. On October 10, 2012

EPA responded with a letter of incompleteness and a request for additional information required

to continue the application revie w process. On behalf of Statoil, ENVIRON International

Corporation (ENVIRON) provided EPA with an initial response letter in December 7 , 2012

, and

another response letter with further information in January 28, 2013 , which included a revised

Air Quality I mpact Analysis (AQIA)

.

On March 14, 2013, ENVIRON’s Bart Brashers received an email from Stan Krivo , requesting

further information/explanations of Statoil’s revised Section 6 of the PSD application (dated

January 28 , 20 13). This letter reiterates EPA’s additional questions, and provides the answers

to each.

Question 1. Stack Exit Parameters

– The following comments are associated with the

modeled stack exit parameters provide in Tables 6.2.3

- 1, 2, and 3.

- The units for the columns Exit Velocity and Exit Temperature are incorrect (meters) in

Tables 6.2.3

- 1 and 2. The correct units should be provided.

ENVIRON has prepared r evised Tables 6.2.3

- 1, 2, and 3 with corrected units and attached them

to this letter

.

Question 2.

- All stacks with horizontal stac k orientation were indicated to be modeled

with an exit velocity of 0.001 m/s. Horizontal stacks in Table 6.2.3

- 3 are not adjusted to

this value and appear to have been used in the impact modeling.

### The exit velocities of the Crewboats and Other Support Ve ssels (OSV), shown in Table 6.2.3

- 3

were not directly used in the CALPUFF modeling. They were only used in the SCREEN3 runs

that were used to determine the initial σ

z 

### values.

Question 3.

- The basis for the stack heights should be provided (e.g., water surface or

vessel deck).

All stack heights are relative to the water surface.

Question 4. Volume Sources

– The following comments are associated with Tables 6.2.3

-

4 and 5.

- The forklifts are associated with the Discoverer America drill ship and their e missions

have been included with the Discoverer America in Attachment 2 emission

calculations. The reason the forklifts are included with the support vessel as a volume

source should be explained.

The forklifts are mobile sources, working on the deck of t he Discoverer Americas. They were

therefore modeled as a volume source, centered on the location of the drilling vessel, and were

not one of the string of volume sources representing the OSV/Crewboats.

The location listed for the source FORK in table 6. 2.3

- 4 of the January 28, 2013 AQIA is

incorrect, but the location in the CALPUFF input files is correct, at LCC coordinates ( 941.964,

-

1186.269 ). Revised tables are included as an attachment to this letter

.

Question 5.

- The vertical dimension of the modeled representative volume sources was

the average height of the offshore support vessels divided by 2.15 (29.5 m or 96.6

feet). The heights of the fleet of available support vessels used to develop this height

should be provided.

The vertical dimensi on (σ

z 

### ) of the volume sources used to represent the OSV/Crewboats was

not , in fact, based on the heights of the vessels as the document indicated. The last sentence

in the paragraph in question (bottom of page 6

- 11 of the January 2013 Revised AQIA) is

inc orrect.

Instead, σ

z 

### was based on two SCREEN3 runs (provided on the modeling DVD). The primary

emitter (main engines) of each vessel was used as a point source in a SCREEN3 run, using

stack parameters provided by support vessel operators and listed in Ta ble 6.2.3

- 3. The

SCREEN3 output file lists the plume parameters at the point of maximum 1

- hour concentration.

From this line of output, the σ

z 

### value for that vessel type was taken. The σ

z 

### from the two

vessels types were then averaged to find the value u sed in the CALPUFF modeling.

The σ

z 

### value used for the crewboats is 3.79 meters, and the value for the OSV is 23.55 meters,

which average to 13.7 meters, the value for σ

z 

### found in the CALPUFF modeling.

### Question 6.

- The volume source heights were indicat ed to be based on SCREEN3 runs

using actual stack parameters, building dimensions bases on ship’s dimensions,

stability of 4, and wind speed of 20 m/s. As noted above for Table 6.2.3

- 3, the crew boat

horizontal stacks should have been modeled with 0.001 m /s exit velocity. Review of the

SCREEN3 modeling files reveals no building dimensions were used for these supply

boats and the selected plume height for the crew boats was associated with 3 stability

and 8 m/s. The bases for the heights (19.41 m) of the volume sources should be

provided and explained.

The SCREEN3 runs did not use a specific wind speed and stability class, as indicated in the

Revised AQIA near the bottom of page 6

- 11 . Instead, the SCREEN3 runs used the more

conservative “full meteorology” approach. This approach finds the maximum concentration over

a wide range of wind speeds and stability classes

. It is a very conservative approach,

guaranteeing the maximum model

- predicted concentration.

The SCREEN3 output file contains, in the same lin e as the σ

z 

### value found at the point of

maximum 1

- hour concentration, the plume height. The center of the plume for the crewboats is

5.39 meters, and the center of the plume for the OSV is 33.42 meters, which average to 19.41

meters. This value was used in the CALPUFF modeling.

Had the SCREEN3 run used an exit velocity of 0.001 m/s for the crewboat , the initial plume

height would have been lower than 5. 39 meters. Using this exit velocity yields 0.12 meters, in

which case the average pl ume height for the crewboat and OSV would have been 16.77 meters,

which is close to the value of 19.41 meters. Given the distance from the source to the nearest

receptors, this error is exceedingly unlikely to change the outcome of the modeling.

T he P rotocol, the original AQIA, and the revised AQIA all took the position that the details of the

initial plume rise are not important at the relevant source

- receptor distances, and that

downwash would not be included in the CALPUFF modeling. EPA did not dispute this

contention. It is therefore consistent that the SCREEN3 modeling did not include building

downwash.

Question 7.

- The horizontal dimension for the representative volume sources are for

both the longitudinal and lateral dimensions. The horizontal dimension modeled w as the

center to center distance between adjacent volume sources divided by 2.15 (5,121 m for

long

- term and 1,664 m for short

- term). This appears not appropriate for the lateral path

dimension and not following the guidance provided in the AERMOD User’s G uide for

volume sources. Further explanation and/or demonstration of the appropriateness of the

support vessels modeling procedure should be provided.

Table 3

- 1 of the AERMOD User Guide lists the suggested σ

y 

### for a “Line Source Represented by

Adjacent Volume Sources (see Figure 1

- 8(a) in EPA, 1995) ” as the length of the side of a box

divided by 2.15. Figure 1

- 8(a) from the ISCST3 Users Guide (EPA ,1995) is shown below:

### Here, W is the length of a side of a b ox, which is equal to the center

- to

- center distance between

adjacent volume sources. As agreed to in the Protocol, the mobile sources (crewboats and

OSV) are modeled using ten (10) volume sources placed along their line of travel during the

time they are within 25 miles of the drilling vessel. The CALPUFF modeling therefore followed

this EPA guidance (the ISCST3 User Guide, essentially reiterated in the AERMOD User Guide).

The essence of this guidance was recently re

- affirmed by the Haul Roads Working Gr oup in

their 2012 document.

Question 8

. Recent Court Decision

- PM2.5 SMC and SIL

- The recent court decision

concerning use of the PM2.5 significant monitoring concentration (SMC) and significant

impact levels (SIL) as the basic for exemption from pre

- c onstruction air quality

monitoring and cumulative NAAQS and PSD increment compliance modeling affects this

application.

- The court has vacated and remained [sic] the PM2.5 SIL. Project impacts less than the

SIL cannot, by itself, be used as justification to eliminate cumulative NAAQS and PSD

increment compliance modeling. Additional information should be provided to support a

conclusion that the project’s impacts would not cause or contribute to a NAAQS or PSD

increment exceedance.

The requested justif ication for using the PM 2.5 

### SIL can be found in the attached report , in

Section 4. The report also provides an analysis of secondary PM 2.5 

### formation in the region, in

Section 5. According to a recently published peer

- reviewed journal article, the region ’s PM 2.5 

### is

### dominated not by ammonium nitrate, but instead by ammonium sulfate. Increases in NOx in the

region are unlikely to bring about corresponding increases in PM 2.5 

### , due to competition for

available ammonia.

Question 9.

- The court also vacated the PM2.5 SMC. Project impacts less than the SMC

can no longer be used to exempt the project from pre

- construction ambient air quality

monitoring. If existing air quality observations are proposed in lieu of pre

- construction

monitoring, supporting inform ation should be provided to demonstrate that existing

ambient air quality data would provide representative or conservative ambient

concentrations for the impact area.

The requested supporting information in lieu of pre

- construction monitoring can be found in the

attached memo, in Section 4.

Question 10. PSD Class I Area Air Quality Related Values (AQRV) Assessment

- The

federal land managers for the Breton Class I area should be provided an opportunity to

review and comment on the updated PSD Class I area AQRV impact analyses.

ENVIRON will cc: the relevant FLM (Jill Webster) with this correspondence, and verify she has

received the January 2013 AQIA.

Please contact me if you have further questions.

Sincerely,

Bart Brashers, PhD

425

- 412

- 1812

bbrashers@environcorp.com

### 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

### 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 Developing 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 1.00 188.32 607 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

### Table 6.2. 3

- 4



### Volume Source Stack Parameters for Support Vessels

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 13.7

VOL02 

### 900.98

- 1186.58 19.41 0 

### 2382 13.7

VOL03 

### 906.101

- 1186.55 19.41 0 

### 2382 13.7

VOL04 

### 911.223

- 1186.51 19.41 0 

### 2382 13.7

VOL05 

### 916.345

- 1186.47 19.41 0 

### 2382 13.7

VOL06 

### 921.467

- 1186.43 19.41 0 

### 2382 13.7

VOL07 

### 926.589

- 1186.39 19.41 0 

### 2382 13.7

VOL08 

### 931.71

- 1186.35 19.41 0 

### 2382 13.7

VOL09 

### 936. 84

- 1186.31 19.41 0 

### 2382 13.7

VOL10 941. 9 6 4

- 1186. 26 9 19.41 0 

### 2382 13.7

FORK (a) 941 .964

- 1186.269 2.74 0 10 1.4

(a) Forklift applicable only to the Discoverer Americas analysis



### Table 6.2. 3

- 5

Volume Source Stack Parameters for Support Vessels

Used in Short

- Term CALPUFF Modeling Analysis

ID X

- UTM Y

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

VOL01 895.858

- 1186.624 19.41 0 774 13.7

VOL02 897.523

- 1186.619 19.41 0 774 13.7

VOL03 899.188

- 1186.613 19.41 0 774 13.7

VOL04 900.853

- 1186.608 19.41 0 774 13.7

VOL05 902.518

- 1186.603 19.41 0 774 13.7

VOL06 904.184

- 1186.597 19.41 0 774 13.7

VOL07 905.849

- 1186.592 19.41 0 774 13.7

VOL08 907.514

- 1186.587 19.41 0 774 13.7

VOL09 909.179

- 1186.581 19.41 0 774 13.7

VOL10 910.844

- 1186.576 19.41 0 774 13.7

FORK (a) 941 .964

- 1186.269 2.74 0 10 1.4

(a) Forklift applicable only to the Discoverer Americas analysis