From: Bart Brashers [bbrashers@environcorp.com]

Sent: Thursday, June 13, 2013 8:54 PM

To: Krivo, Stan

Cc: Shepherd, Lorinda

Subject: RE: Statoil's 24 April 2013 Response to EPA Comments - Remaining 

Outstanding Items

Attachments: Discoverer_Americas-top_and_side_views.pdf

Stan,

If we steer clear of the SCREEN3 method and return to using traditional guidance for the VOLUME 

source initial height and sigma-z values, I believe that would alleviate (circumnavigate?) Comments 2, 5, 

and 6. Do you agree? In the modeling we submitted, the VOLUME sources use a height of 19.4 m and a 

sigma-z of 13.7 m (bold to ease comparison with alt. numbers below).

Using the average height (29.5 m) of the offshore support vessels and the concepts presented by the 

Haul Roads Workgroup, would give a VOLUME source height of 1.7 × 29.5 / 2 = 24.9 m and a sigma-z of 

1.7 × 29.5 / 2.15 = 23.2 m. The 1.7 factor comes from a paper that looked at unpaved roads, which may 

or may not be applicable. If we discard the 1.7 factor, we’d get a VOLUME source height of 29.5 / 2 = 

14.7 m and a sigma-z of 29.5 / 2.15 = 13.6 m. That’s pretty close to the 19.4 m and 13.7 m values used 

in the submitted modeling. A height of either 14.7 m or 19.4 m would both be released into the first 

CALMET layer (0 to 20 m) so I believe the answers from CALPUFF would be very similar.

The Forklift aboard the Discover Americas operates on the lowest deck (closest to the water) called the 

“MN DK” (Main Deck) in the attached PDF. The last page gives the heights in mm of each deck (the 

numbers to the right, relative to the beam that’s under water, not relative to the water line). The 

lifeboats are on C Deck, elevation 29100 mm, and the Forklift is on the Main Deck, elevation 19500 mm 

– so the decks are 9.4 meters apart. We rounded that to 10m, and set the height of the Forklift to 

2.74m (10m less than the lifeboats at 12.74m). So maybe we’re a bit off (less than 1 meter) but I don’t 

think it would make much difference in the outcome, especially considering its emissions are so much 

smaller than other units. I hope this information takes care of Comment 4.

For Comment 7 regarding the VOLUME source spacing, I was in a bit of a quandary when I tried to think 

of what the width of the line source should be. In reality, the boats would almost certainly not follow 

the same path every time, because there’s no road or train track to constrain them. I would think that 

for the Annual run, one could assume them to be wider than for the short-term run. For the annual run 

it’s probably not as critical either, considering the max impacts are two orders of magnitude lower than 

the NO2 or PM2.5 SILs.

For the short-term run, we first tried using the most conservative assumption we could, that the 

OSV/crewboats were stationary at the 25-mile point. That proved too conservative, so we assumed the 

ships were moving at a conservatively slow 8 knots (15 km/hr) which is less than their stated maximum 

speeds of 12 knots (Peyton Candies, an OSV) or 21 knots (Sybil Graham, a crewboat). We therefore 

distributed the VOLUME sources over 15 km (not 40 km = 25 nautical miles, as in the annual run), which 

makes the distance between the VOLUME sources 1,665 m (sigma-y = 774 m) when using 10 VOLUME 

sources. The ships’ beams are 18.3 m and 10.4 m. We’d have to use 1000 VOLUME sources to get the 

inter-source distance down to 16.65 m (which is close to the average of 18.3 m and 10.4 m). Using 1000 

VOLUME sources, in addition the all the POINT sources, would make CALPUFF run very slowly – seems 
burdensome to me. It’s really one ship moving, not a line of cars, trucks, or trains, so it seems like we 

should use a width of the source that’s wider than the width of the ships themselves. But I can’t think of 

what we could use – do you have a suggestion for the width? Maybe use 100 VOLUME sources, so the 

“width” is 151 m to account for the lack of road (meandering) and yet have CALPUFF run in a reasonable 

amount of time?

I will call you on Monday morning, and together we can come up with an approach that will work, given 

the amount of conservativism we’ve already got in the modeling.

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

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

Sent: Wednesday, June 12, 2013 10:54 AM

To: Bart Brashers

Cc: Shepherd, Lorinda

Subject: Statoil's 24 April 2013 Response to EPA Comments - Remaining Outstanding Items

Bart,

This is a follow up to today’s telephone call on the remaining outstanding concerns on the air 

quality analyses supporting the Statoil permit application. The following provides the original 

review comments from our 14 March 2013 letter that remain outstanding based on review of 

the responses provided in ENVIRON’s 24 April 2013 letter. In BOLD print following each original 

review comment are my concerns. Further explanation, justification, or information is needed 

to resolve these issues. 

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.

- 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.

[Comment 2: Remains Outstanding – Although the exit velocities for the Crew and OSV 

provided in this table were only used in the SCREEN3 model to determine the initial Sigma 

Z values, the stacks are indicated to be horizontal. The horizontal stack guidance 

procedure should have been used to determine the input velocities for SCREEN3.

In addition, an explanation should be provided as to why the volume source guidance for 

estimating the initial vertical dimension (Sigma Z) for multiple volume sources was not 

used.] 
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.

[Comment 4: Remains Outstanding – Although the forklifts were mobile source on the 

deck of the Discoverer America, the basis for the release height (2.74 m) and initial vertical 

Sigma Z (1.4 m) should be provided. These values do not appear to follow the suggested 

procedure for estimating these dimensions for volume sources.] 

- 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.

[Comment 5: Remains Outstanding – The vertical dimension was not based on the 

suggested procedures as indicated in the text but associated plume height determined from 

SCREEN3 runs at the point of maximum concentration using questionable stack 

parameters. As noted in comment 2 above, the reason the volume source guidance for 

estimating the initial vertical dimension (Sigma Z) for multiple volume sources was not 

used 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.

[Comment 7: Remains Outstanding – The recommended spacing between individual 

volume sources representing a line source should not be greater than twice the width of the 

line source. The guidance indicates larger spacing can be used if the ratio of the minimum 

source-receptor separation and spacing between individual volume sources is greater than 

about 3. In this application the largest spacing between volume sources is 5,121 m (longterm assessment) and the nearest receptor is much further away than 3 times this spacing 

(15,453 m). For this condition the suggested procedure to estimate the initial lateral 

dimension was associated with Figure 1-8(b) in the reference EPA 1995 document where 

the increased spacing between volume sources relative to the width of the line source is 

offset by increased emission rate for each individual volume sources modeled. This 

procedure does not appear to have been used in the modeling. . In addition, the reason 

different volume line source configurations were used for long-term and short-term 

modeling 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.
[Comment 6: Remains Outstanding – The concerns noted for Comment 2 above also apply 

to this comment.

Concerning the building dimensions, they should have been included in the SCREEN3 

runs. Unlike the CALPUFF modeling where the source-receptor distances are large, the 

source-receptor distances for the SCREEN3 are not large and the initial plume rise is 

important to the analyses. ]

I suggest we have a telephone discussion of these items to ensure we understand the issues and 

determine any needed actions

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)

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