From: Krivo, Stan

Sent: Thursday, March 14, 2013 10:09 AM

To: Bart Brashers

Cc: Shepherd, Lorinda

Subject: Statoil Updated Air Quality Analysis - Remaining Issues

Bart,

I have reviewed the second response to our review comments on Statoil’s Title V/PSD Permit 

Application for OCS drilling and exploration activities in the Eastern Gulf of Mexico (EGOM) and 

the updated air quality modeling analysis (UAQMA) contained as Attachment 1 to the response 

letter. To complete this review, the following items from the UAQMA need further 

information/explanations.

Revised Section 6 - Air Quality Impact Assessment (January 2013) 

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. 

- All stacks with horizontal stack 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 basis for the stack heights should be provided (e.g., water surface or vessel deck).

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 emissions 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 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 horizontal dimension for the representative volume sources are for both the longitudinal 

and lateral dimensions. The horizontal dimension modeled was the center to center distance 

between adjacent volume sources divided by 2.15 (5,121 m for long-term and 1,664 m for shortterm). This appears not appropriate for the lateral path dimension and not following the 

guidance provided in the AERMOD User’s Guide for volume sources. Further explanation 

and/or demonstration of the appropriateness of the support vessels modeling procedure should be 

provided.

- The volume source heights were indicated 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.
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-construction air quality monitoring and cumulative NAAQS and 

PSD increment compliance modeling affects this application.

- The court has vacated and remained 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 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 information 

should be provided to demonstrate that existing ambient air quality data would provide 

representative or conservative ambient concentrations for the impact area.

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.

Please let me know if you have any questions.

Thanks...sjk

Stanley J. Krivo

U.S. Environmental Protection Agency

Atlanta Federal Center, 61 Forsyth Street, SW

Atlanta, GA 30303

404/562-9123 (Phone) 404/562-9091 (Fax)