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 prese nted 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 int o 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 t he 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, espec ially 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 sou rce 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 ru n. 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/c rewboats 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 (S ybil 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

– seemsburdensome 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 us e

– 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 c an 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 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

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. Furth er 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 provi de 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 mo deling. [ 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 sourc es 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 e mission 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 th e 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 vo lume 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 vertica l 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 dimensi ons. 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 short

term). 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 betwee n 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 v olume sources is greater than
about 3. In this application the largest spacing between volume sources is 5,121 m (long

term assessment) and the nearest receptor is much further away than 3 times this spacing (15,453 m). For this condition the suggested p rocedure 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 eac h 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 ha ve 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 t he 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 S CREEN3

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 the se 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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