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Kelly, Shaheerah

From: Stewart, Kathleen

Sent: Tuesday, October 07, 2014 7:56 AM

To: Stewart, Kathleen

Subject: Fw: McElmo flare concern?

Attachments: McElmo_SCREEN.zi

****************************************************

Children's Environmental Health and Schools Team, EPA Region 9

75 Hawthorne St (CED-4)

San Francisco, CA 94105

Phone (415) 947-4119

Fax: 947-3583

I work a part-time schedule. I am available Tuesdays and Thursdays, from 6:30AM-3:00PM, and Wednesdays 

from 8:30-12:30. Should you need assistance at other times, you can contact Jacquelyn Hayes at (415) 972-

3259.

----- Forwarded by Kathleen Stewart/R9/USEPA/US on 10/07/2014 07:56 AM -----

From: Kathleen Stewart/R9/USEPA/US

To: Scott Bohning/R9/USEPA/US@EPA, 

Date: 04/28/2006 08:42 AM

Subject: Re: McElmo flare concern?

Scott - did you ever hear back from these guys?

************************************* 

Katie Stewart 

Environmental Scientist 

Air Division, Permits Office 

75 Hawthorne Street 

US EPA, Region 9 

San Francisco, CA 94105-3901 

(415) 947-4119 

(415) 947-3579 fax 

Scott Bohning/R9/USEPA/US

Scott Bohning/R9/USEPA/US 

04/06/2006 03:09 PM

To "John Bunyak" <John_Bunyak@nps.gov>, John_Notar@nps.gov

cc Kathleen Stewart/R9/USEPA/US@EPA

Subject McElmo flare concern?

John & John -

I hope you're both doing well -- I'll probably see you in Denver last week of April.

ExxonMobil has to do a PSD permit for McElmo Main Flare as part of a consent decree. This source is probably too small 
2

to be of interest to you, but they should have contacted you anyway. Please let us know if you have a concern over this 

source, or if they could be excused from AQRV analysis.

It's in Utah, SW corner. Long & Lat is: -109.2038, 37.26 

Their worst-case emission estimates for this flare: SO2 320.00 tons/yr; CO 659.1 tons/yr; NOx 76.8 tons/yr

According to their SCREEN3 modeling, maximum impacts are about 1 km away, and are below the Class II significance 

levels, and way below NAAQS. 

The nearest Class I areas are Canyonlands NP (UT) and Mesa Verde NP (CO), and are within 100 km (but more than 50 

km). I did quick rerun of SCREEN3 for 40-50 km, and source is below Class I significance levels.

Source contact info:

"Neil Ryan" <neil.j.ryan@exxonmobil.com>

US Production OIMS - ER Supervisor

281/654-1042

Thanks...

- Scott B.

P.S. Katie - sorry for the delay, I meant to get this out Monday a.m.

=+=+=+=+=+=+=+=+=+=+=+=+=+=+= 

Scott Bohning 

U.S. EPA Region 9, AIR-7 

bohning.scott@epa.gov 

415/947-4127 fax-3579

Attached ZIP file contains:

- Model Input Data and Summary Results_3-28-05.doc - ExxonMobil's SCREEN3 results

- mcelmo_c1.gif - my location map showing source and Class I areas

- ME300.dat, me300.out , ME443.dat, ME443.out - my SCREEN3 input & output for 300 and 443 BTU/scf heat content 

scenarios

- McElmo_SCREEN3_SCALE.XLS - my SCREEN3 results scaled to emission rates, comparison to sig levels

(Note: Attachments with names ending in ".zi" are ZIP archives; 

to use, detach and rename to have ".zip" ending. EPA e-mail 

administrators strip .zip files from all outgoing and incoming 

e-mail, on the grounds that several years ago there was a flurry 

of viruses/worms contained in e-mailed .zip files, e.g. MyDoom.)

(See attached file: McElmo_SCREEN.zi)
McElmo Main Flare Model and Assumptions 

- 1 - 

McElmo Main Flare Dispersion Model Results and Assumptions 

Project 

In order to comply with Section V, Paragraph 14a of the 2005 Consent Decree between 

Mobil Exploration and Producing U.S. Inc. and the United States Environmental Protection 

Agency (EPA) an air quality analysis was performed in accordance with the requirements of 

40 C.F.R. §52.21. The purpose of this document is to summarize the assumptions and 

processes utilized to complete the air quality analysis. 

A preliminary analysis was performed using the SCREEN3 dispersion modeling program. 

This model was used to run the emissions associated with the McElmo Main Flare, to 

evaluate NOx, CO, and SO2. The following section pertains to the input data and 

assumptions used to model the emissions using SCREEN3. 

Model Input Data 

The dispersion modeling program was run based on two different lower heating values 

(LHV) of the gas being burned at the McElmo Main Flare. The lowest value input into 

SCREEN3 was 300 BTU/scf, which is the lowest allowable LHV as stated in 40 CFR 

60.18(c)(3)(ii). The higher value utilized was 443 BTU/scf, which is the lowest of the four 

most recent actual plant gas samples from McElmo. The four analyses are dated 4/28/04, 

5/27/04, 8/29/04, and 9/29/04; and their LHV values in BTU/scf were 443, 505, 512, and 

453, respectively. The 443 BTU/scf LHV was utilized due to the assumption that it would 

provide the least amount of heat rise, thus producing the lowest effective release height. 

The maximum flare rate utilized was 689,423 acf/hr (618,104 scf/hr), which assumes that the 

flare is operating at 14.83 MCFD for the entire year. The flare rate value of 618,104 scf/hr 

was based on the assumption that the new flare tip will be 24 inches in diameter and will 

have a flare tip exit velocity of 64.74 ft/s. This exit velocity is below the maximum exit 

velocity as specified by 40 CFR 60.18, which is 66.98 ft/s. 

The heat released from the flare tip was then calculated and converted to a rate of calories per 

second based on the conversion of 1 BTU = 252.1644 calories. The equation used for this 

calculation is as follows: 

s

LHV V cal heat cal s

3600

( )( )(252.1644 ) ( / ) 

 Where: 

 LHV = lower heating value of gas burned (BTU/scf) 

 V = 618,104 scf/hr. 

The actual flare stack height of 195 feet was taken from drawing D-SA-107 as provided by 

Zeeco, Inc. from 1991. This measurement was field verified to ensure proper stack height. 

The emission factors for NOx and CO were derived by the Chemical Section of the Texas 

Commission on Environmental Quality NSR Division based on data published in the 1983 
McElmo Main Flare Model and Assumptions 

- 2 - 

Chemical Manufacturer's Association document entitled "A Report On A Flare Efficiency 

Study." The factors used were as follows: 

 NOx = 0.0641 lb/MMBTU 

 CO = 0.5496 lb/MMBTU. 

Therefore, the equation used to calculate the emission rate for NOx and CO contaminants at 

the specified LHV is as follows: 

s

hr

lb

g

MMBTU

lb EF

BTU

MMBTU

scf

BTU LHV

hr

scf rate g s V

3600

* 453.59 * *

10 ( / ) * *

6 

 Where: 

 V = 618,104 scf/hr 

 LHV = lower heating value of gas burned (BTU/scf) 

 EF = emission factor (lb/MMBTU). 

Recent tests at the McElmo site indicate the plant inlet gas contains approximately 450 ppm 

H2S. However, it was assumed that the flared gas contains 700 ppm H2S on the SCREEN3 

SO2 dispersion model. This H2S value was used in order to provide a conservative estimate 

of SO2 emissions from the flare. The emission rate was calculated as follows: 

lbSO hr

scf mol MMparts

scf hr ppm lb molSO

rate 73.06 2 /

379 / 1

618,104 / 700 64 / 2  

  

Model Runs

Once all assumption and data was obtained, the SCREEN3 model was run for each 

contaminant at the LHV of 300 BTU/scf and 443 BTU/scf. The model was run using the full 

meteorology scenario and was set to provide contaminant concentrations at ground level. 

The model results are based on the simple terrain inputs as detailed in the assumptions and 

utilizing the rural option based on the area of the flare location. 
McElmo Main Flare Model and Assumptions 

- 3 - 

Results

The results provided by SCREEN3 are based on 1-hour averaging period concentrations. 

The one hour estimates were converted to longer averaging periods utilizing the following 

EPA factors: 0.9 (3-hr); 0.7 (8-hr); 0.4 (24-hr); and 0.08 (Annual). The results are 

summarized in Tables 1 & 2 below. The equation used for converting to longer averaging 

periods is as follows: 

concentration( g / m ) F *C 3  

 Where: 

 F = EPA conversion factor 

 C = 1-hour averaging period concentration (g/m3

). 

Table 1: Maximum Contaminant Concentrations at 300 BTU 

Pollutant Averaging 

Period 

Max. Modeling 

Concentration @ 

1097 meters (g/m3) 

PSD Modeling 

Significance 

Levels (g/m3) 

NAAQS (g/m3) 

NOx Annual 0.15 1 100 

CO 8-hour 11.35 500 10,000 

 1-hour 16.21 2,000 40,000 

SO2 Annual 0.93 1 80 

 24-hour 4.65 5 365 

 3-hour 10.47 25 1300 

Table 2: Maximum Contaminant Concentrations at 443 BTU 

Pollutant Averaging 

Period 

Max. Modeling 

Concentration @ 

1075 meters (g/m3) 

PSD Modeling 

Significance 

Levels (g/m3) 

NAAQS (g/m3

) 

NOx Annual 0.17 1 100 

CO 8-hour 12.90 500 10,000 

 1-hour 18.43 2,000 40,000 

SO2 Annual 0.72 1 80 

 24-hour 3.58 5 365 

 3-hour 8.06 25 1300 
McElmo Main Flare Model and Assumptions 

- 4 - 

Summary

In order to prepare a conservative model for the prediction of emissions from the McElmo 

Main Flare several assumptions were made. Many of these assumptions were made with the 

intent of providing conservative estimates including: 

1. The lowest heat value rating for the gas at McElmo to lower the effective release 

height of the emissions produced by the McElmo Main Flare. 

2. The maximum design flare rate of 14.83 MCFD. 

3. The H2S concentration of 700 ppm instead of the actual measured value of 

approximately 450 ppm. 

Emission limitations established by the Consent Decree for the McElmo Main Flare are 60 

tons per year of SO2, 73 tons per year of CO, 13.4 tons per year of NOx, and 94.5 tons per 

year of VOC. The worst-case conditions based on this maximum flare rate of 14.83 MCFD 

and a LHV of 443 BTU/scf result in emissions of 320.00 tons per year of SO2, 659.1 tons per 

year of CO, and 76.8 tons per year of NOx. With these worst-case estimates as mentioned 

above, the modeling results do not meet the NAAQS concentrations as can be seen above in 

Tables 1 & 2. These very conservative assumptions model release conditions over five times 

greater than current air permit limits. In addition, the actual field conditions are not capable 

of sustaining a flow rate of 14.83 MCFD. 

McElmo Flare - comparison of distant impact to Class I significance levels

Scaling of 1 g/s SCREEN3 run, automated distances 40 km - 50 kmSCREEN3 averaging time conversion

simple terrain complex terrainmulitply 1-hr by: mulitply 24-hr by:

averaging ti

mconversion f

auncerainty averaging ti

mconversion factor

110 143 0.9 0.1 3 46 0.76 0.2 6 48 0.7 0.2 8 3

24 0.4 0.2 24 1

8760 0.08 0.02 8760 0.32

SCREEN3 maxin 40-50 km

0.2782 Class I Class II

pollutant avg.time conv. factor emission rat

eprediction sig. level sig. leve

300 BTU SO2 700pp

m 3 0.9 9.21 8.5672 ok 25 512 

SO2 700pp

m 24 0.4 9.21 3.9622 ok 5 91 

SO2 700pp

m 8760 0.08 9.21 1.015 ok 2 20 

SO2 3 0.9 10.52 9.7462 ok 25 512 SO2 24 0.4 10.52 4.4862 ok 5 91 SO2 8760 0.08 10.52 1.1198 ok 2 20 NOx 8760 0.08 1.5 0.3982 ok 2.5 25 CO 1 1 12.84 13.1182 CO 8 0.7 12.84 9.2662 

SCREEN3 maxin 40-50 km

0.2243

pollutant avg.time conv. factor emission rat

eprediction

443 BTU SO2 700pp

m 3 0.9 9.21 8.5133 ok 25 512 

SO2 700pp

m 24 0.4 9.21 3.9083 ok 5 91 

SO2 700pp

m 8760 0.08 9.21 0.9611 ok 2 20 

SO2 3 0.9 10.52 9.6923 ok 25 512 SO2 24 0.4 10.52 4.4323 ok 5 91 SO2 8760 0.08 10.52 1.0659 ok 2 20 NOx 8760 0.08 2.21 0.4011 ok 2.5 25 CO 1 1 18.96 19.1843 CO 8 0.7 18.96 13.4963 
ME300

McElmo Flare 300 BTU

f 10.0 Source type F=flare 

 1.000 emission rate (g/s)

 59.45 flare stack height (m)

 .129887E+08 heat release rate (cal/s)

 .0000 flagpole receptor height (m) 

r Urban/Rural option (If u, delete fumigation block.)

n Consider building downwash?

n Complex terrain heights?

n *Simple terrain heights? (If no, delete lines with *)

 1 Meteorology: 1=full, 2=enter P-G class, 3=enter P-G & u

y Automated distance array?

40000, 60000 {minimum, maximum receptor distances

n Discrete receptors?

n Fumigation calculation? (If urban, delete block.)

n Hardcopy?

Page 1
me300.out

 04/06/06

 14:22:47

 *** SCREEN3 MODEL RUN ***

 *** VERSION DATED 96043 ***

 McElmo Flare 300 BTU 

 SIMPLE TERRAIN INPUTS:

 SOURCE TYPE = FLARE

 EMISSION RATE (G/S) = 1.00000 

 FLARE STACK HEIGHT (M) = 59.4500

 TOT HEAT RLS (CAL/S) = .129887E+08

 RECEPTOR HEIGHT (M) = .0000

 URBAN/RURAL OPTION = RURAL

 EFF RELEASE HEIGHT (M) = 70.9117

 BUILDING HEIGHT (M) = .0000

 MIN HORIZ BLDG DIM (M) = .0000

 MAX HORIZ BLDG DIM (M) = .0000

 THE REGULATORY (DEFAULT) MIXING HEIGHT OPTION WAS SELECTED.

 THE REGULATORY (DEFAULT) ANEMOMETER HEIGHT OF 10.0 METERS WAS ENTERED.

 BUOY. FLUX = 215.357 M**4/S**3; MOM. FLUX = 131.320 M**4/S**2.

 *** FULL METEOROLOGY ***

 **********************************

 *** SCREEN AUTOMATED DISTANCES ***

 **********************************

 *** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***

 DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA

 (M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DWASH

 ------- ---------- ---- ----- ----- ------ ------ ------ ------ -----

 40000. .2782 5 1.0 2.0 10000.0 212.67 1382.31 147.53 NO

 50000. .2430 5 1.0 2.0 10000.0 212.67 1678.21 156.86 NO

 MAXIMUM 1-HR CONCENTRATION AT OR BEYOND 40000. M:

 40000. .2782 5 1.0 2.0 10000.0 212.67 1382.31 147.53 NO

 DWASH= MEANS NO CALC MADE (CONC = 0.0)

 DWASH=NO MEANS NO BUILDING DOWNWASH USED

 DWASH=HS MEANS HUBER-SNYDER DOWNWASH USED

 DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED

 DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB

 ***************************************

 *** SUMMARY OF SCREEN MODEL RESULTS ***

 ***************************************

 CALCULATION MAX CONC DIST TO TERRAIN

 PROCEDURE (UG/M**3) MAX (M) HT (M)

 -------------- ----------- ------- -------

 SIMPLE TERRAIN .2782 40000. 0.

 ***************************************************

 ** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **

 ***************************************************

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ME443

McElmo Flare 443 BTU

f 10.0 Source type F=flare 

 1.000 emission rate (g/s)

 59.45 flare stack height (m)

 .191799E+08 heat release rate (cal/s)

 .0000 flagpole receptor height (m) 

r Urban/Rural option (If u, delete fumigation block.)

n Consider building downwash?

n Complex terrain heights?

n *Simple terrain heights? (If no, delete lines with *)

 1 Meteorology: 1=full, 2=enter P-G class, 3=enter P-G & u

y Automated distance array?

40000, 60000 {minimum, maximum receptor distances

n Discrete receptors?

n Fumigation calculation? (If urban, delete block.)

n Hardcopy?

Page 1
ME443.out

 04/06/06

 14:28:18

 *** SCREEN3 MODEL RUN ***

 *** VERSION DATED 96043 ***

 McElmo Flare 443 BTU 

 SIMPLE TERRAIN INPUTS:

 SOURCE TYPE = FLARE

 EMISSION RATE (G/S) = 1.00000 

 FLARE STACK HEIGHT (M) = 59.4500

 TOT HEAT RLS (CAL/S) = .191799E+08

 RECEPTOR HEIGHT (M) = .0000

 URBAN/RURAL OPTION = RURAL

 EFF RELEASE HEIGHT (M) = 73.2591

 BUILDING HEIGHT (M) = .0000

 MIN HORIZ BLDG DIM (M) = .0000

 MAX HORIZ BLDG DIM (M) = .0000

 THE REGULATORY (DEFAULT) MIXING HEIGHT OPTION WAS SELECTED.

 THE REGULATORY (DEFAULT) ANEMOMETER HEIGHT OF 10.0 METERS WAS ENTERED.

 BUOY. FLUX = 318.009 M**4/S**3; MOM. FLUX = 193.915 M**4/S**2.

 *** FULL METEOROLOGY ***

 **********************************

 *** SCREEN AUTOMATED DISTANCES ***

 **********************************

 *** TERRAIN HEIGHT OF 0. M ABOVE STACK BASE USED FOR FOLLOWING DISTANCES ***

 DIST CONC U10M USTK MIX HT PLUME SIGMA SIGMA

 (M) (UG/M**3) STAB (M/S) (M/S) (M) HT (M) Y (M) Z (M) DWASH

 ------- ---------- ---- ----- ----- ------ ------ ------ ------ -----

 40000. .2243 5 1.0 2.0 10000.0 234.08 1382.49 149.12 NO

 50000. .2001 5 1.0 2.0 10000.0 234.08 1678.35 158.35 NO

 MAXIMUM 1-HR CONCENTRATION AT OR BEYOND 40000. M:

 40000. .2243 5 1.0 2.0 10000.0 234.08 1382.49 149.12 NO

 DWASH= MEANS NO CALC MADE (CONC = 0.0)

 DWASH=NO MEANS NO BUILDING DOWNWASH USED

 DWASH=HS MEANS HUBER-SNYDER DOWNWASH USED

 DWASH=SS MEANS SCHULMAN-SCIRE DOWNWASH USED

 DWASH=NA MEANS DOWNWASH NOT APPLICABLE, X<3*LB

 ***************************************

 *** SUMMARY OF SCREEN MODEL RESULTS ***

 ***************************************

 CALCULATION MAX CONC DIST TO TERRAIN

 PROCEDURE (UG/M**3) MAX (M) HT (M)

 -------------- ----------- ------- -------

 SIMPLE TERRAIN .2243 40000. 0.

 ***************************************************

 ** REMEMBER TO INCLUDE BACKGROUND CONCENTRATIONS **

 ***************************************************

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