ENVIRON International Corp. 19020 33rd Avenue West, Suite 310 , Lynnwood, WA 98036

V +1 425.412.1800 F +1 425.412.1840

environcorp.com

July 12, 2013

Via Electronic Mail

Stan Krivo

EPA Region 4

Krivo.Stanley@epa.gov

Re: Statoil PSD Application – Response to comments

Dear Mr Krivo:

This letter is in response to your email to me dated Thu July 11, 2013. I include your text in blue, 

with my responses below each section.

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 procedure are 

still applicable and should be addressed.

A revised Table 6.3.1-1 is included below, with annual average taken from the CALPUFF simulation 

that used short-term emission rates, included on the modeling DVD in the directories “calpuffdiscoverer-st.epa” and “calpuff-maersk-st.epa”. Recall that the short-term CALPUFF modeling used 

point sources to represent the crew boats and OSVs, locating them at the end of the 25 nautical mile 

line. Because the short-term emission rates exceed the long-term emission rates, this is a 

conservative over-estimate of the annually average concentrations, yet they do not exceed the 

relevant SILs. Using the short-term emission rates avoids the need to submit another modeling DVD.

By using point sources instead of volume sources, we effectively side-step the above concerns about 

the initial plume height, sigma-y, and sigma-z values. The only remaining volume source is used to 

characterize the relatively minor emissions from the forklift and cement handling. A revised Table 

6.2.3-4 follows.
Stan Krivo - 2 - July 12, 2013

Table 6.3.1-1

Maximum CALPUFF-Predicted Class II Concentrations

Criteria 

Pollutant

Averaging 

Period

Developer Max. 

Concentration (μg/m3)

Discoverer Americas

Max. 

Concentration (μg/m3)

Modeling 

Significance 

Level 

(μg/m3)

Monitoring 

DeMinimus 

Concentration 

(μg/m3)

NO2 a 1-hr 5.7 7.3 7.5 c None c

Annual 0.22 0.28 1.0 14

PM2.5

24-hr b 0.08 0.10 1.2 d 4 d

Annual 0.0061 0.0069 0.3 d None

Notes:

a Annual NOX was assumed to be 75 percent converted to NO2, and use the short-tem emission rates instead of the longterm emission rates. One-hour NO2 model prediction based on the three year average of the maximum daily model-predicted 

1-hour NOX concentration at each receptor location and 80 percent conversion to NO2 (Tier II of EPA’s June 28, 2010 memo 

“Guidance Concerning the Implementation of the 1-hour NO2 NAAQS for the Prevention of Significant Deterioration Program.”

b 100th percentile (maximum) values are presented (not 98th percentile) using direct PM2.5 emissions only.

c Interim SIL, established June 28, 2010 in the memo “Guidance Concerning the Implementation of the 1-hour NO2 NAAQS for 

the Prevention of Significant Deterioration Program”. The 1-hour NO2 Monitoring DeMinimus level has not yet been proposed.

d The PM2.5 SILs and SMC were vacated on January 22, 2013,but presented here for comparison.

- 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.

A revised Table 6.2.3-3 is included below. Note that the CALPUFF modeling used the correct values 

of 0.001 m/s for all horizontal stacks, which can be verified in Block 13b of the files calpuff.year.inp.

Table 6.2.3-4

Volume Source Stack Parameters for Miscellaneous Sources

Used in Visibility and Long-Term CALPUFF Modeling Analysis

ID X-UTM Y- UTM Height (m) Elev (m) Sigma Y (m) Sigma Z (m)

MISC (a) 941.964 -1186.269 1.5 2.74 10 1.4

(a) MISC used to represent cement handling and the forklift, applicable only to the Discoverer Americas
Stan Krivo - 3 - July 12, 2013

Table 6.2.3-3

Support Vessel Point Source Stack Parameters

Used in CALPUFF Modeling Analysis

Stack Modeling 

ID

X-Coord 

(LCC)

Y-Coord

(LCC)

Height

(ft)

Elev.

(ft)

Diameter 

(ft)

Exit 

Velocity 

(ft/s)

Exit 

Temp 

(K)

Orientation

OSV (Main #1) OSV1 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical

OSV (Main #2) OSV2 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical

OSV (Main #3) OSV3 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical

OSV (Main #4) OSV4 895.858 -1186.624 57.04 0 1.33 157.32 718 Vertical

Crewboats (Main 

#1) C1 895.858 -1186.624 3.28 0 1.00 0.001 718 Horizontal

Crewboats (Main 

#2) C2 895.858 -1186.624 3.28 0 1.00 0.001 607 Horizontal

Crewboats (Main 

#3) C3 895.858 -1186.624 3.28 0 1.00 0.001 607 Horizontal

Crewboats (Main 

#4) C4 895.858 -1186.624 3.28 0 1.00 0.001 607 Horizontal

Crewboats 

(Generator #1) CG1 895.858 -1186.624 3.28 0 0.33 0.001 610 Horizontal

Crewboats 

(Generator #2) CG2 895.858 -1186.624 3.28 0 0.33 0.001 610 Horizontal

- The application should explain why the stack heights provided in Table 6.2.3.-3 are lower 

than the average height of the support and crew boats provided in Table 6.2.3-4. 

As can be seen in the PDF diagrams of the Peyton Candies1 and Sybil Graham2 available on the 

Internet, the support vessel’s exhaust is near the top of the pilot house, while the crew boat’s exhaust 

is about 1 meter above the water line (horizontal exhaust from the side of the vessel). 

The modeling IDs VOL01 through VOL10 in Table 6.2.3-4 will no longer be relevant, because the 

CALPUFF model run used to assess annual average used point sources instead of volume sources 

to characterize the crew boats and OSVs.

- 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 comments 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 suggested 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.

 

1 http://www.ottocandies.com/specs/peyton.pdf

2 http://www.grahamgulf.com/sybil_graham.htm
Stan Krivo - 4 - July 12, 2013

- 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 and 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.

Because the CALPUFF runs used to evaluate annual average impacts compares to the annual SILs 

use point sources instead of volume sources to represent the crew boats and OSVs, these 

comments are no longer relevant. 

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 refer to the email from ENVIRON’s Michael Carbon, dated April 25, 2013, to EPA. I include 

the relevant sections here:

Maersk Developer

Will any welding activities be conducted during the drilling campaign?

Yes, welding occurs as part of regular maintenance activities. Rig operators estimate that up to 

240 pounds of welding electrodes could be used per 180-day drilling campaign. Electricity for 

welding is provided by the main engines on the drilling vessel. ENVIRON has estimated emissions 

from the welding activities to be less than 0.01 tpy of PM/PM10/PM2.5 and approximately 7 lb/yr of 

total HAP. Detailed emission calculations for welding activities are attached to this email.

Since potential emissions of regulated air pollutants are less than 2 tpy, and HAP emissions are less 

than 1,000 lb/yr, the emission levels from welding activities are considered insignificant per 40 CFR 

71.5(c)(11)(ii). There are no applicable regulations that would apply to the maintenance welding 

activities.

Detailed emission calculations for welding activities and application forms that required an update are 

attached to this email.3

Will any painting (spray or roller) activities be conducted during the drilling campaign?

Yes, painting occurs as part of regular maintenance activities. Rig operators estimate that up to 

380 gallons of paint coating and 310 gallons of paint thinner could be used per 180-day drilling 

campaign. Paint is applied using both brush/roller and sprayer depending on the size and location 

that needs to be painted; however, ENVIRON has assumed 100 percent of the paint is applied by 

spray to conservatively account for particulate matter emissions generated from paint overspray.

MSDS information (Percent Solids, VOC content, HAP content, etc.) was obtained for each paint 

coating and thinner used on the drill rig. ENVIRON has estimated emissions from painting in Table 1 

below. Detailed emission calculations and application forms that required updating are attached to 

this email.

 

3 Included as an attachment to this e-letter as well.
Stan Krivo - 5 - July 12, 2013

Since potential HAP emissions (Xylene) are above the 1,000 lb/yr insignificance level, painting 

activities are not considered an insignificant activity. There are no applicable regulations that would 

apply to the maintenance painting activities.

Table 1. Maersk Developer – Painting Emissions

Pollutant Emissions

(tpy)

PM10 0.3

PM2.5 0.1

VOC 1.5

Xylene 0.8

Transocean Discoverer Americas

Will any welding activities be conducted during the drilling campaign?

Yes, welding occurs as part of regular maintenance activities. Rig operators estimate that up to 

50 pounds of welding electrodes could be used per 180-day drilling campaign. Electricity for welding 

is provided by the main engines on the drilling vessel. ENVIRON has estimated emissions from the 

welding activities to be less than 0.002 tpy of PM/PM10/PM2.5 and less than 2 lb/yr of total HAP.

Since potential emissions of regulated air pollutants are less than 2 tpy, and HAP emissions are less 

than 1,000 lb/yr, the emission levels from welding activities are considered insignificant per 40 CFR 

71.5(c)(11)(ii). There are no applicable regulations that would apply to the maintenance welding 

activities. Detailed emission calculations for welding activities and application forms that required an 

update are attached to this email.4

Will any painting (spray or roller) activities be conducted during the drilling campaign?

Yes, painting occurs as part of regular maintenance activities. Rig operators estimate that up to 

250 gallons of paint coating and 250 gallons of paint thinner could be used per 180-day drilling 

campaign. Paint is applied using both brush/roller and sprayer depending on the size and location 

that needs to be painted; however, ENVIRON has assumed 100 percent of the paint is applied by 

spray to conservatively account for particulate matter emissions generated from paint overspray.

MSDS information (Percent Solids, VOC content, HAP content, etc.) was obtained for each paint 

coating and thinner used on the drill rig. ENVIRON has estimated emissions from painting in Table 2 

below. Detailed emission calculations and application forms that required updating are attached to 

this email.

Since potential emissions of regulated air pollutants are less than 2 tpy, and individual HAP 

emissions are less than 1,000 lb/yr, the emission levels from painting activities are considered 

insignificant per 40 CFR 71.5(c)(11)(ii). There are no applicable regulations that would apply to the 

maintenance painting activities.

 

4 Included as an attachment to this e-letter as well.
Stan Krivo - 6 - July 12, 2013

Table 2. Transocean Discoverer – Painting Emissions

Pollutant Emissions

(tpy)

PM10 0.2

PM2.5 0.1

VOC 1.5

Xylene 0.4

Please contact me as soon as possible if you need further clarification. 

Sincerely,

Bart Brashers

Atmospheric Scientist