From: Bart Brashers [bbrashers@environcorp.com]

Sent: Friday, July 12, 2013 9:04 PM

To: Krivo, Stan

Cc: Shepherd, Lorinda; Michael Carbon; Kyle Heitkamp
Subject: RE: Statoil EGOM PSD Application: Revised Air Quality Impact Assessment

Attachments: Maersk_Developer

- Emissions_and_Forms.pdf;
Transocean_Discoverer_Americas

- Emissions_BACT_and_Forms.pdf;
Response_Stan_Krivo_2013

- 07

- 12.pdf

Categories: OCS

Stan,

Enclosed please find a letter, along with some relevant attachments, addressing your concern s. Please contact me as soon as possible if there are any other outstanding issues. If I happen not to be at my desk when you call, please press 7 to be transferred to my mobile phone (or dial my mobile directly, number below).

Bart

Bart Brashers | Atmospheric Scientist Senior Manager, ENVIRON International Corporation

19020 33 rd Ave W Ste 310 | Lynnwood WA 98036

T: +1 425

- 412

- 1 812 | F: +1 425

- 412

- 1840 | M: +1 206

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- 2606 bbrashers@environcorp.com

From: Krivo, Stan [mailto:Krivo.Stanley@epa.gov]

Sent: Thursday, July 11, 2013 11:14 AM

To: Bart Brashers

Cc: Shepherd, Lorinda Subject: RE: Statoil EGOM PSD Application: Revised Air Quality Impact Assessment

Bart,



### This is a follow up to today’s telephone discussion concerning the revised air quality modeling
section of the application. The revised application is in response to our rev iew comments on the previous version of the application that addressed issues with the method and procedures
used to model the support vessels as a volume line source. The following provides the
remaining concerns with the revised modeling section.

Revised Section 6

- Air Quality Impact Assessment (June 2013)

Revised Support and Crew Boat Modeling

– The revised modeling for support vessels and crew boats appears to uses two methodologies; one to address the short term standard and one for the long

- term annual standard. The modeling to assess the long

- term standard appears to be unchanged from the previous version of the application (i.e., volume line source from the drilling

### vessel extending 25 nautical miles towards the nearest shoreline/Class I area) while the short

term modeling had the support and crew boats modeled as a point sources located 25 nautical miles from the drilling vessel at the closest point to the shore line and PSD Class I area.

- EPA’s comments on the previous version of the application requested an explanation and/or demonstration of the appropriateness of the input parameters used in volume line source modeling procedure. EPA did not request a more conservative modeling approach for the support vessels and crew boats.

- It appears that the volume line source modeling for the long

- term standard was unchanged from the previous version of this application. Therefore, our previous comments on the appropriateness of the volume line source initial input parameters and modeling pr ocedure are still applicable and should be addressed.

- The reason the horizontal stacks in Table 6.2.3

- 3 do not have their exit velocities reduced as in

Table 6.2.3

- 2 should be provided.

- The application should explain why the stack heights provided in T able 6.2.3.

- 3 are lower than the average height of the support and crew boats provided in Table 6.2.3

- 4.

- The volume source input parameters provided in Table 6.2.3

- 4 do not appear appropriate because they do not agree with ENVIRON’s response to our comm ents on the previous version of the application. The proper input parameters should be identified and explained.

- The average height of the offshore support vessels was given as 29.5 meters in a response to our initial review comments. Based on suggeste d procedures for estimating Sigma z, this height yields a value of 13.7 meters.

- In another response to the previous review comments the actual heights were based on the ship diagrams yielding 18.0 and 7.6 meters or an average of 12.8 meters. The heights based on ship diagrams appear more appropriate. This would yield a Sigma z of 5.95

meters.

- The support ships beam widths were indicated to be 18.3 and 10.4 meters. Following suggested procedures this would yield an average path width of 14.4 meters an d a Sigma y of 6.7 meters.

- The volume height was set to the averaged heights of the crew and OSV boats. The application provided these heights as 5.39 and 33.42 meters but a response to our previous comments indicates these heights as plume heights from SCREEN3 runs.

Welding and Painting

– The revised application has included welding and painting as a new source of project emissions. The anticipated operational characteristics of these activities and associated emission estimates should be provided to support exclusion from the modeling analyses.

Please let me know of any questions. Thanks...sjk

From: Bart Brashers [ mailto:bbrashers@environcorp.com ]

Sent: Thursday, June 27, 2013 4:40 PM

To: Krivo, Stan; Shepherd, Lorinda; Jill Webster ( Jill_Webster@fws.gov )

Cc: Donald Evans; Michael Carbon; Brian Glover; Kyle Heitkamp Subject: Statoil EGOM PSD Application: Revised Air Quality Impact Assessment

Stan,En closed please find an revised Air Quality Impact Assessment that reflects the changes to the Statoil

PSD Application, as per our recent discussions. It refers to the PM2.5 Assessment that you’ve seen
before, which is also enclosed. I trust that this vers ion of the assessment will allow the application
process to proceed. A revised modeling DVD will be sent under separate cover to you today.

Jill,

The portions of the enclosed Air Quality Impact Assessment that pertain to Class I Area visibility
degrad ation and deposition have not changed since last you saw it, but I wanted to make sure you had a

chance to comments on the final version.

Bart

Bart Brashers | Atmospheric Scientist Senior Manager, ENVIRON International Corporation

19020 33 rd Ave W Ste 310 | Lynnwood WA 98036

T: +1 425

- 412

- 1812 | F: +1 425

- 412

- 1840 | M: +1 206

- 550

- 2606 bbrashers@environcorp.com



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