From: Webster, Jill <jill_webster@fws.gov>

Sent: Thursday, May 15, 2014 4:35 PM

To: Bart Brashers

Cc: Shepherd, Lorinda; Michael Carbon

Subject: Re: Statoil PSD: Revised VISIBILITY modeling

Categories: OCS

Lori,

The Fish and Wildlife Service does not object to the revised visibility modeling and the method 

used to estimate the impacts from the support vessels. However, we do not agree with results of 

greater than 5% change in extinction. But due to the conservatism of the emissions modeled (as I 

understand, all boats operating at 100% load, simultaneously) and the temporary nature of the 

project, we do not object to the revised Class I analyses. 

Please contact me directly, if you have any questions or if I have misinterpreted the information 

related to this permit application.

On Wed, May 14, 2014 at 6:14 PM, Bart Brashers <bbrashers@environcorp.com> wrote:

Jill,

For the pending Statoil PSD permit modification (OCS-EPA-R4012), please find enclosed a 

revised CALPUFF visibility (VIS) analysis.

Our recent submittal to EPA included short-term Class I/II SILs analysis modeling runs that 

used the maximum 1-hour emission rate (and “passed” the SILs test) but did not “pass” the VIS 

criteria. That scenario was conservative, modeling 3 OSVs and 1 crewboat as point sources at 

the end of the 25-mile line closest to port, with 1-hour emission rates for the full 24 hours of a 

VIS run. Because this conservative scenario did not meet the VIS criteria, we needed to relax 

one of the conservative assumptions, and we chose to develop 24-hour emission rates. We 

assumed the OSV/Crew vessels would operate at 75% load for 6 of 24 hours, and at 50% load 

for the other 18 of 24 hours.

EPA is concerned that because the support vessels are not owned or operated by Statoil directly, 

we would have difficulty demonstrating compliance through monitoring and recordkeeping. 
The enclosed modeling analysis relaxes a different conservative assumption – modeling mobile 

sources as stationary point sources. Following the Haul Roads Working Group report, we used 

a series of 100 volume sources to represent the support vessels. The initial plume dimensions 

(sigma-y and sigma-z) were set using the width and height of a support vessel, divided by 4.3. 

The release height was set at half the height of the support vessel. The emission rates used were 

the maximum 1-hour emission rates, evenly distributed over the 100 volume sources.

This modeling technique should allay EPA’s concerns, because the OSV/Crew vessels use the 

same emission rates for the VIS modeling as for the SILs modeling. Hopefully this will 

alleviate the need for a separate permit condition to track OSV/Crew vessel engine loads. The 

SILs modeling (point sources) is still more conservative for 24-hour averages than the VIS 

modeling (volume sources), so that should not cause any issues with EPA.

The results of the revised VIS modeling are as follows:

5.03 = 2001 98th percentile

4.32 = 2002 98th percentile

4.73 = 2003 98th percentile

18.95 = highest value

19 = number of days over 5%

5 = number of days over 10%

These can be found in the file “vis.method8.bret.results.txt”, and are extracted from the 

CALPOST runs. I’ve included the CALPUFF input and list files, but not the large binary CON 

files. If you would prefer, I can copy the full collections of input/output files to a DVD and 

mail it to you.

Please contact me if you have any questions, and email your acceptance of this alternate VIS 

modeling to Lori Shepherd at EPA after your review.
Bart

Bart Brashers | Atmospheric Scientist

Senior Manager, ENVIRON International Corporation

19020 33rd 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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--

Jill Webster, Environmental Scientist

US Fish and Wildlife Service

National Wildlife Refuge System

Branch of Air Quality

7333 W. Jefferson Ave., Suite 375

Lakewood, CO 80235-2017

(303) 914-3804

fax: (303) 969-5444