### McElmo materials Scott Bohning Scott Bohning to: Cleveland Holladay 02/22/2012 04:19 PM Cc: Andrew Chew

Cleve -

I found an e-mail I sent to Tom Hormel 2011-04-26 stating that one DVD one be sufficient, and he should send it to Andrew.... so I suppose he has it.

Also, here are other materials I have on McElmo, other than what Andrew attached to the meeting invitation ("McElmo Creek Main Flare SO2 Modeling_042211.pdf" and "Modeling Transmittal Letter_060111.pdf:)

- Scott B.

modeling_report_eml.txt modeling_report_eml.txt McElmo_NO2_SO2.txt McElmo_NO2_SO2.txt McElmo Creek Main Flare PSD App_041108.pdf

flare_parms_eml_101222.txt flare_parms_eml_101222.txt Flare Stack Parameter Est imation_122010.xls Flare Stack Parameter Estimation_122010.xls Flare Stack Parameter Estimation.pdf

AERMOD Results_1 hr SO2.pdf SCREEN3 SO2 Runs_2008.pdfe20120222 att modeling_report_eml Date: 06/01/2011 04:04 PM From: Tom Hormel To: Scott Bohning Cc: pflynn Subject: RE: 1-Hour SO2 Modeling Report for McElmo Creek Gas Plant
Scott,
At long last, attached are the final PDF version of the 1-hour SO2 modeling report, using AERMOD, for the McElmo Creek Gas Plant and the transmittal letter. Per your instructions below, two hard copies of the report, with one report containing a modeling DVD, has been sent by FedEx to Andrew Chew with delivery scheduled for approximately 10:30 AM PDT on Friday, June 3.
The modeling files are rather large and not readily amenable to sending by e-mail. However, the DVD accompanying the hard copies of the report contain pertinent AERMAP, meteorological and AERMOD input/output files.
Please contact me if you have any questions.

Thomas Hormel
McVehil-Monnett Associates, Inc. Vice President & Sr. Project Manager 44 Inverness Drive East, Bldg C. Englewood, CO 80112 303.790.1332

mcvehil-monnett.com

Page 1e20120222 att McElmo_NO2_SO2 sjb notes, 2010-11-30
Resolute Natural Resources Company’s McElmo Creek Main Flare
language on 1-hour NO2 and SO2 NAAQS modeling
Resolute used the SCREEN3 model to assess ambient air impacts from the McElmo Creek Main Flare. Since that work was done, EPA promulgated a new 1-hour NO2 NAAQS and a new 1-hour SO2 NAAQS.
To estimate the flare's annual NO2 impact, Resolute used the SCREEN3 model. SCREEN2 output is on a 1-hour averaging time basis; Resolute applied an EPA-recommended factor of 0.08 to convert the results to an annual average, and also applied an EPA-recommended factor of 0.75 to estimate the fraction of NO that converts to NO2. The same modeling results can be used to estimate 1-hour NO2 impacts simply by omitting these conversion factors, thus leaving the results on a 1-hour basis and assuming that 100% of emitted NO converts to NO2. The maximum estimated impact from SCREEN3 was 2.5 μg/m3 (see Table 7-2, pdf.69). The Significant Impact Level (SIL) for 1-hour NO2 is 4 ppb, or about 7.5 μg/m3. Since the estimated impacts are less than the SIL, the flare has been shown not to cause or contribute to a 1-hour NO2 NAAQS violation. The situation is similar for SO2, except that there is no NO/NO2 conversion factor. The maximum modeled 1-hour SO2 impact for the flare was 11.6 μg/m3 (see Table 7-3, pdf.69). The interim SIL for 1-hour SO2 is 3 ppb, or about 7.8 μg/m3. Since the estimated impacts are above the interim SIL, the flare may have a significant contribution to a 1-hour SO2 NAAQS violation, if the latter is uncovered by cumulating modeling. (If estimated impacts are above the SIL, then a cumulative modeling analysis must be performed, which includes nearby sources in addition to the flare. SCREEN3 is a screening model, more conservative than the refined AERMOD model. Modeling the flare with AERMOD could show lower concentrations.)

Page 1e20120222 att flare_parms_eml_101222 Scott Bohning date: 12/22/2010 02:29 PM From: thormel@mcvehil-monnett.com To: Scott Bohning/R9/USEPA/US@EPA Cc: pflynn@rnrc.net Subject: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack
Scott,
We have modeled the flare stack at the McElmo Creek Gas Plant near Aneth, UT, using the AERMOD as we discussed recently. The flare stack was characterized as a point source by estimating effective stack diameter and stack height with stack velocity and temperature set at values consistent with SCREEN3 guidance. The flare stack was modeled at four flare gas heat content values (i.e., 300, 443. 538.8 and 682.4 BTU/SCF) with a constant SO2 emission rate based on 700 ppmv H2S. The modeled stack parameters and emission rate for each of these four flare gas heat content cases is summarized in the attached table. The SCREEN3 output from the modeling report submitted in 2008 is also attached to show the consistency between the model input for AERMOD and the previous SCREEN3 modeling.
We ran the AERMOD both in the flat and complex terrain modes and get mixed results when comparing the maximum modeled 1-hour SO2 impacts to the 1 hour SO2 SIL of 7.9 ug/m^3. These modeling results are:
1. In the flat terrain mode, maximum 1--hour SO2 impacts are below the 1-hour SO2 SIL for the 443, 538.8 and 682.8 BTU/SCF cases, but slightly over for the 300 BTU/SCF case (i.e., 8.5 vs. 7.9 ug/m^3) 2. In the complex terrain mode, maximum 1-hour SO2 impacts are above the 1-hour SO2 SIL for the 300, 433 and 538.8 BTU/SCF cases and slightly below for the 682.4 BTU/SCF case; the highest maximum 1-hour SO2 impact is 22 ug/m^3 for the 300 BTU/SCF case and drops down to 15 ug/m^3 for the 433 BTU/SCF case.
If we rely on the flat terrain mode runs which would be consistent with the simple terrain assumed for the 2008 SCREEN3 modeling, we demonstrate modeled 1-hour SO2 impacts below the SIL by citing the results for the three higher heat content cases. Recent monthly flare gas analysis data suggest that the lowest heat content of the flare gas is approximately 500 BTU/SCF and that the 300 BTU/SCF is an unrealistically conservative case. However, if we rely on the complex terrain results, regional modeling with background SO2 emission sources may be necessary because of the results described above.
We would like to discuss these modeled impacts to determine if we need to pursue getting a background SO2 emission inventory at your convenience.
Thank you for your assistance,

Tom Hormel McVehil-Monnett Associates (303) 790-1332, ext. 134 thormel@mcvehil-monnett.com

Page 1Assumptions: Actual Stack Height (m.), H s : 59.45 Stack Temperature ( o K), T s : 1273 Stack Velocity (m/s), V s : 20.0 Flare Gas Flow Rate (scf/hr): 618104.0 Ambient Temperature ( o K), T: 294.3 (Assumed as 70.0 o F.)

1. H sl , Effective Stack Height (m.) = H s + (4.56 x 10 -3 ) * (H r /4.1868) 0.478 where, H r = Net Heat Release (Joules/sec) = (1 - F) H
F = Radiative Loss Factor 1 : 0.0 % H = Heat release at from flared gas at a particular heat content, in joules/sec 1 BTU = 1055.0 Joules = 252 Calories

1 Estimated heat content of flare gas is an indicator of sensible heat, not requiring a radiative loss factor.

Heat Content Net Heat Release, H r Effective Stack Height, H sl (BTU/SCF) (BTU/sec) (Joules/sec) (Joules/sec) (m.) 300 51508.7 54341643.3 54341643.33 70.91 443 76061.1 80244493.3 80244493.32 73.25 538.8 92509.6 97597591.4 97597591.43 74.61 682.4 117165.0 123609124.7 123609124.7 76.42

2. d s , Effective Stack Diameter (m.) = 0.03249 * ((H r /V s ) * (T s /(T * (T s - T)))) 0.5
where H r , V s , T s and T are input variables with assigned values described above

Heat Content Net Heat Release, H r Stack Velocit y , V s Stack Temp., Ts Ambient Air Tem p ., T Effective Stack Diameter, d s (BTU/SCF) (Joules/sec) (m/sec) ( o K) ( o K) (m.) 300 54341643.33 20.0 1273.0 294.3 3.561 443 80244493.3 20.0 1273.0 294.3 4.327 538.8 97597591.4 20.0 1273.0 294.3 4.772 682.4 123609124.7 20.0 1273.0 294.3 5.370

3. Flare Stack Parameters Used for Each Flare Gas Heat Content Scenario in AERMOD

Heat Content Effective Stack Height, H sl Effective Stack Diameter, d s Stack Temp., Ts Stack Velocity, V s SO 2 Emission Rate (BTU/SCF) (m.) (m.) ( o K) (m/sec) (g/s) 300 70.908 3.561 1273.0 20.00 9.21 443 73.254 4.327 1273.0 20.00 9.21 538.8 74.609 4.772 1273.0 20.00 9.21 682.4 76.421 5.370 1273.0 20.00 9.21 Heat Release, H 

### Flare Stack Parameters with Assumed Stack Velocit y , Hei g ht and Temperature as a Function of Heat Release for AERMODAssumptions: Actual Stack Height (m.), H s : 59.45 Stack Temperature ( o K), T s : 1273 Stack Velocity (m/s), V s : 20.0 Flare Gas Flow Rate (scf/hr): 618104.0 Ambient Temperature ( o K), T: 294.3 (Assumed as 70.0 o F.)

1. H sl , Effective Stack Height (m.) = H s + (4.56 x 10 -3 ) * (H r /4.1868) 0.478 where, H r = Net Heat Release (Joules/sec) = (1 - F) H
F = Radiative Loss Factor 1 : 0.0 % H = Heat release at from flared gas at a particular heat content, in joules/sec 1 BTU = 1055.0 Joules = 252 Calories

1 Estimated heat content of flare gas is an indicator of sensible heat, not requiring a radiative loss factor.

Heat Content Net Heat Release, H r Effective Stack Height, H sl (BTU/SCF) (BTU/sec) (Joules/sec) (Joules/sec) (m.) 300 51508.7 54341643.3 54341643.33 70.91 443 76061.1 80244493.3 80244493.32 73.25 538.8 92509.6 97597591.4 97597591.43 74.61 682.4 117165.0 123609124.7 123609124.7 76.42

2. d s , Effective Stack Diameter (m.) = 0.03249 * ((H r /V s ) * (T s /(T * (T s - T)))) 0.5
where H r , V s , T s and T are input variables with assigned values described above

Heat Content Net Heat Release, H r Stack Velocit y , V s Stack Temp., Ts Ambient Air Tem p ., T Effective Stack Diameter, d s (BTU/SCF) (Joules/sec) (m/sec) ( o K) ( o K) (m.) 300 54341643.33 20.0 1273.0 294.3 3.561 443 80244493.3 20.0 1273.0 294.3 4.327 538.8 97597591.4 20.0 1273.0 294.3 4.772 682.4 123609124.7 20.0 1273.0 294.3 5.370

3. Flare Stack Parameters Used for Each Flare Gas Heat Content Scenario in AERMOD

Heat Content Effective Stack Height, H sl Effective Stack Diameter, d s Stack Temp., Ts Stack Velocit y , V s SO 2 Emission Rate (BTU/SCF) (m.) (m.) ( o K) (m/sec) (g/s) 300 70.908 3.561 1273.0 20.00 9.21 443 73.254 4.327 1273.0 20.00 9.21 538.8 74.609 4.772 1273.0 20.00 9.21 682.4 76.421 5.370 1273.0 20.00 9.21 Heat Release, H 

### Flare Stack Parameters with Assumed Stack Velocit y , Hei g ht and Temperature as a Function of Heat Release for AERMODComplex TerrainMaximum2005 2006 2007 2008 2009 ImpactValueUnits(μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3)300 BTU/SCF 22.01 20.75 21.42 21.51 21.16 22.01 Yes433 BTU/SCF 15.10 12.74 12.42 13.32 13.15 15.10 Yes538 BTU/SCF 11.51 9.79 9.30 9.72 10.87 11.51 Yes682 BTU/SCF 7.80 6.97 6.21 6.33 8.11 8.11 YesFlat TerrainMaximum2005 2006 2007 2008 2009 ImpactValueUnits(μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3) (μg/m3)300 BTU/SCF 5.46 5.90 6.26 6.73 8.56 8.56 Yes433 BTU/SCF 4.82 4.74 4.82 4.63 5.90 5.90 No538 BTU/SCF 4.48 4.16 4.39 3.87 4.80 4.80 No682 BTU/SCF 4.02 3.38 3.87 3.37 4.24 4.24 No1-Hour SO2Significant Impact Level (SIL):7.9μg/m33.0ppbFuel Heat ContentScenarioMeteorological Data YearMODELED MAXIMUM 1-HOUR SO2IMPACTS FROM THE McELMO CREEK GAS PLANTFLARE STACK USING AERMODGreaterThan SIL?GreaterThan SIL?Fuel Heat ContentScenarioMeteorological Data Year

# R ESOLUTE

N ATURAL 

### R ESOURCES


### for Resolute Natural Resources Company 1675 Broadway, Suite 1950 Denver, CO 80202



# McElmo Creek Unit Oil Production Facility - Main Flare, Gas Compression Facility 1-Hour SO 2 

# Modeling with AERMOD Resolute Natural Resources Company

April 2011 MMA Project Number 2440-10

by McVehil-Monnett Associates, Inc.

44 Inverness Drive East, Building C Englewood, CO 80112

### i TABLE OF CONTENTS

Page No.



### 1.0 INTRODUCTION.............................................................................................. 1-1 2.0 PROJECT DE SCRIPTION............................................................2-1 3.0 MAIN FLARE EMISSIONS.............................................................................. 3-1 3.1 CRITERIA POLLUTANTS............................................................................... 3-2 4.0 EXISTING ENVIRONMENT ........................................................................... 4-1 4.1 TOPOGRAPHY ................................................................................................. 4-1 4.2 AIR QUALITY .................................................................................................. 4-1 4.3 AREA CLIMATE AND METEOROLOGY ..................................................... 4-2 5.0 IMPACT ASSESSMENT APPROACH ............................................................ 5-1 5.1 AIR QUALITY MODEL DESCRIPTION ........................................................ 5-2 5.2 MODEL INPUT ................................................................................................. 5-2 5.3 METEOROLOGICAL DATA ........................................................................... 5-3 5.4 SOURCE CHARACTERISTIC S AND EMISSION RATES............................ 5-5 5.4.1 Fuel Rate and Heat Release ................................................................................. 5-5 5.4.2 Flare Height ......................................................................................................... 5-6 5.4.3 Modeled Emission Rates......................................................................................5-6 5.5 RECEPTOR SELECTION................................................................................. 5-7 5.6 BACKGROUND MODELED SOURCES ........................................................ 5-8 6.0 AIR QUALITY IMPACTS ................................................................................ 6-1 6.1 SULFUR DIOXIDE (SO 2 

### )................................................................................. 6-2 7.0 REFERENCES ............................................................................7-1

LIST OF TABLES

TABLE 3-1 PRE-PROJECT & POST-PRO JECT ACTUAL & PTE EMISSIONS TABLE 3-2 MAIN FLARE CRITERI A POLLUTANT EMISSION LIMITS TABLE 4-1 SO 2 

### 1-HOUR MONITORING IN THE McELMO CREEK AREA TABLE 4-2 JOINT FREQUENCY DISTRIBU TION OF WIND SPEED AND DIRECTION CANYONLANDS AIRPORT, UTAH TABLE 4-3 ANNUAL STABILITY CLASS DISTRIBUTION AT CANYONLANDS AIRPORT,UT TABLE 4-4 MONTHLY AVERAGE TEMPERA TURE & TOTAL PRECIPITATION AT BLANDING, UT TABLE 5-1 SUMMARY OF NATIONAL AM BIENT AIR QUALITY STANDARDS AND PSD INCREMENTS TABLE 5-2 ESTIMATED FLARE STAC K PARAMETERS FOR AERMOD INPUT TABLE 5-3 MODELED STACK PARAMETERS AND EMISSIONS FOR THE MAIN FLARE

### ii TABLE 5-4 MODELED BACKGROUND SOURCE INPUT TABLE 6-1 COMPARISON OF MODELED CUMULATIVE SO 2 

### IMPACTS TO THE 1- HOUR SO 2 

### NAAQS - FLAT TABLE 6-2 COMPARISON OF MODELED CUMULATIVE SO 2 

### IMPACTS TO THE 1- HOUR SO 2 

### NAAQS - ELEV

LIST OF FIGURES

FIGURE 2-1 LOCATION MAP OF McELM O CREEK OIL PRODUCTION FACILITY FIGURE 2-2 FLOW DIAGRAM OF EXISTI NG GATHERING SYSTEM OPERATIONS FIGURE 4-1 WIND ROSE OF CANYONLA NDS AIRPORT, UTAH METEOROLOGICAL DATA FIGURE 5-1 1-HOUR SO 2 

### MODELED RECEPTOR GRID INCLUDING FINE GRIDS FIGURE 6-1 MAXIMUM MODELED 1-HOUR SO 2 

### IMPACTS WITH THE FLARE AND BACKGROUND SOURCES - 300 BTU/SCF CASE (ELEV) FIGURE 6-2 MAXIMUM MODELED 1-HOUR SO 2 

### IMPACTS WITH THE FLARE AND BACKGROUND SOURCES - 682.4 BTU/SCF CASE (ELEV)

LIST OF APPENDICES

APPENDIX A DVD WITH AERMOD MODEL INPUT & OUTPUT FILES, METEOROLOGICAL DATA AND AERMAP FILES

### 1-1 1.0 INTRODUCTION

Resolute Natural Resources Company (Resolute) is submitting this supplemental air modeling study for 1-hour SO 2 

### impacts at the request of EPA Region IX during a meeting held on November 30, 2010. A Prevention of Significant Deterioration (P SD) permit application for its
Main Flare at the McElmo Creek Oil Production Facility, located on the Navajo Nation near Aneth, Utah were submitted on March 22, 2007 to meet the terms of a Consent Decree (DOJ Case No. 90-5-2-1-2237, filed June 8, 2005). This Consent Decree was issued to the previous owner/operator of the facility, Exxo nMobil Corporation (ExxonMobil).

The PSD permit application document presented a facility process description for existing operations, criteria pollutant permit emission limits for the Main Flare, a Best Available Control Technology (BACT) analysis fo r the Main Flare, air modeling methodology, and air modeling results. Impacts were evaluate d in both Class I and II areas. A revised permit application was submitted in April 2008 that responded to EPA Region IX comments concerning increased emissions due to processing flare gas with a higher BTU content than previ ously cited. This air modeling study is intended as a supplement to the already submitted permit application because none of the other non-air modeling information has changed.

This air modeling study for 1-hour SO 2 

### impacts is submitted to demonstrate modeled compliance
to the 1-hour SO 2 

### ambient air quality standard of 196 μg/m 3 

### , effective on August 23, 2010 with a detailed description of the fina l rule published in the Federal Register dated June 22, 2010. An ambient air quality st andard for 1-hour NO 2 

### of 188 μg/m 3 

### also became effective on April 12, 2010 with a detailed description of the final rule published in the Federal Register dated February 9, 2010. Both of these st andards were promulgated after the most recent revision of the PSD permit application submitted in April 2008.

An additional modeling study for the 1-hour NO 2 

### standard is not n ecessary because the SCREEN3 modeling presented in Section 7.1 of the PSD permit application document indicated
a maximum 1-hour NO 2 

### impact of 2.5 μg/m 3 

### , well below the significant impact level (SIL) of 7.5 μg/m 3 

### (4 ppb). However, the maximum 1-hour SO 2 

### impact presented in Section 7.2 of the application document was 11.6 μg/m 3 

### , above the SIL of 7.9 μg/m 3 

### (3 ppb).

### 2-1 2.0 PROJECT DESCRIPTION

This section presents an overview of the Mc Elmo Creek Oil Production Facility operations, including the gas compression plant.

Currently, produced fluids at the oil production facility are processed, sold, and re-injected through a series of satell ite facilities, main tank batteries, and injection plants. Produced fluids are gathered and separated at one of eleven satellite facilities located throughout the field. Gases
from the satellite facilities are directed to the gas compression plant, and liquids are pumped to
one of four central tank batteries . Gases sent to the gas compression plant are compressed, dried through a glycol dehydrator, ble nded with carbon dioxide (CO 2 

### ), and re-injected into the field. Liquids are further separated at the central tank batteries, with oil being sold and transported through a pipeline system. Water from the central tank batteries is pumped to the water flood injection plant.

The Main Flare at the gas compression plant co mbusts gases that have been bypassed around the plant’s electric-driven compressors or that come through various em ergency relief valves in the compression plant. Additionally, the vent stream from the plant’s glycol dehydrator is directed
to the Main Flare.

A location map of the McElmo Oil Production Faci lity is presented in Figure 2-1. A flow diagram of the facility’s gather ing system operations is presente d in Figure 2-2, illustrating the flow through the satellite facilities, central tank batteries, water flood injection plant, and gas compression plant.Figure 2-2Block Flow Diagram of ExistingGathering System OperationsMcElmo Creek Oil Production Unit

### 3-1 3.0 MAIN FLARE EMISSIONS

As requested in the EPA Region IX comment lett er of May 22, 2006, this se ction presents preand post-project actual emissions, as well as pre- project estimates of the potential to emit (PTE) for all criteria pollutants, including particulate matter (PM 10 

### and PM 2.5 

### ) and lead. Pre- and postproject gas flow rates to the flare are also incl uded. Per EPA’s comment letter, pre-project is defined as prior to the gas compression facility being dismantled in 1997, and post-project is defined as subsequent to the gas plant being dismantled. Thus, pre-project emission estimates provided in Table 3-1 are based on 1996 gas flare rates and a conser vative gas analysis from that year and post-project emission estimates ar e based on the 2005 emi ssion inventory, updated by gas analysis data from 2005-08. The post-project emissions presented in Table 3-1 reflect the updated estimates from 2005-08 gas analyses data.

As clarified in the EPA Region IX comment lett er of November 8, 2006, post-project PTE is for the period following the dismantling of the gas pl ant, but prior to the imposition of the Consent Decree limits. Therefore, the post-project PTE emissions provided are based on 2003 flare emissions data multiplied by a PTE factor of 1.2 since the annual flare rate in 2003 was the highest of the five year period 2001-2005. Upda ted post-project PTE emissions based on more recent gas analyses from late 2005 through 2008 and the natural gas flow rate from 2003 multiplied by 1.2 are also provided. These post -project PTE determinations were made in accordance with the methodology outlined in 40 CFR § 63.760(a)(1)(i)(B) (E&P MACT) and past Texas Commission on Environmental Quality (TCEQ) guidance on PTE calculations for oil & gas operations. Applicable calculation me thodology with input data used to estimate emissions are presented in Appendix B of the PSD permit application document.

The gas flow rates to the flare used for the emission estimates are 1,145.96 MMscf in 1996 (for both actual and PTE emissions), 727.704 in 2005 (rounded off to 730.0 MMSCF) for postproject actual emissions, and 1,070.366 MMscf for post-project PTE emissions. Because the flare is only used for emergency relief and to c ontrol dehydrator still vent emissions, the daily rates vary.

### 3-2 Table 3-1 Pre-Project and Post-Project Actual and PTE Emissions

Criteria Pollutant Pre-Project Actual Emissions (tpy) Pre-Project PTE 1 

### (tpy) Post-Project Actual Emissions (tpy) Post-Project PTE 2 

### (tpy) CO 159.2 159.2 82.5 135.1 NO x 

### 29.3 29.3 15.2 24.8 VOC 183.6 183.6 91.7 151.8 SO 2 

### 138.1 138.1 30.1 44.2 Lead 0.00021 0.00021 0.000109 0.000179 PM 10 

### 3.2 3.2 1.7 2.7 PM 2.5 

### 3.2 3.2 1.7 2.7

1 Pre-project PTE is equivalent to 1996 actual emission estimates.
2 Post-project PTE is estimated by identifying the maximum annual gas flow rate from the most recent five-year

period with available data (i.e., 2001 – 2005) and multiplying by a contingency factor of 1.2 to provide a worstcase post-project PTE estimate. The maxi mum gas flow year of 2003 was select ed as the basis for this estimate. The maximum BTU content from 2005-08 gas analyses data (682.4 BTU/SCF) was assumed for emission estimates.



### 3.1 CRITERIA POLLUTANTS

Table 3-2 presents a summary of criteria pollutant emission limits for the Main Flare as listed in Paragraph 9.a of Exxon Mobil’s Consent Decree. Due to the higher BTU content occurring since issuance of the Consent Order, Reso lute is requesting revised emission limits corresponding to the last column of Table 3-1.

Table 3-2 Main Flare Criteria Pollutant Emission Limits 1



### Pollutant tons/year 2



### SO 2 

### 60
CO 73
NOx 13.4
VOC 95.4
1. As listed in Paragraph 9.a of Consent Decree (DOJ Case No. 90-5- 2-1-2237) 2. Cumulative 365-day rolling average.

### 4-1 4.0 EXISTING ENVIRONMENT

4.1 TOPOGRAPHY

The McElmo Creek Oil Production Facility is lo cated on Navajo Nation land in southeastern Utah, in San Juan County, near the town of An eth. The gas compression facility is located approximately 23 km (14 miles) northwest of th e Utah / Colorado border and 4.8 km (3 miles) north of State Highway 262. Arches National Pa rk and Canyonlands Nati onal Park are located to the northwest, approximately 160 km (100 mile s) and 96 km (60 miles), respectively. Mesa Verde National Park is located approximately 60 km (38 miles) east of the gas compression facility site. The western boundary of the Canyon of the Ancients National Monument is approximately 16 km (10 miles) northwest of the plant site.

Elevations around the gas compression plant range from 5,500 feet to 5,900 feet. Terrain generally increases in both the north and south directions from the east-west valley formed by the San Juan River. Ground cover is relatively sparse because of the semiarid climatic conditions surrounding the gas co mpression facility site.

4.2 AIR QUALITY

Background SO 2 

### air quality monitoring data for 2008-2010 are presented in Table 4-1. No site or area-specific data are availabl e for southeastern Utah; therefore, air quality data gathered from the monitoring station located at Salt Lake City International Airport, and the monitoring station located at USBR – Shiprock (Farmington, NM) are used as conservative indicators of background air quality. However, the Salt Lake City data are from an urban location and not as representative of the rural conditions surrounding the McEl mo Creek Gas Plant as those surrounding the USBR Shiprock site . Therefore, the background c oncentrations from the USBR Shiprock site are used to repr esent conditions existing near the McElmo Creek Gas Plant. Per EPA’s guidance memo of August 23, 2010, the first tier approach for selection of monitored background SO 2 

### concentration to add to modeled impact s is to use the highest daily maximum hourly concentration. As a result, the highest daily maximum hourly concentration of 79 μg/m 3 

### from the USBR Shiprock site is the appropria te background concentration for the 1-hour SO 2 

### modeling.

### 4-2 Table 4-1. SO 2 

### 1-Hour Monitoring in the McElmo Creek Area. Daily Maximum Concentration 99 th Percentile NAAQS 2

Pollutant Monitor Location/County 1 Averaging Period Year ( ppm / μg/m 3 ) ( ppm / μg/m 3 ) ( ppm / μg/m 3 )

2008 0.131 / 343 0.057 / 149
2009 0.069 / 181 0.038 / 100 Salt Lake City International AP/Salt Lake 1-hour

2010 0.031 / 81 0.029 / 76 0.075 / 196.5

2008 0.028 / 73 0.020 / 52
2009 0.030 / 79 0.025 / 65 Sulfur Dioxide

(SO 2 ) USBR Shiprock - Farmington, NM / San Juan 1-hour

2010 0.016 / 42 0.011 / 29 0.075 / 196.5

1 No site-specific data is available. These monitoring locations provide the closest available current data. 2 To attain this standard, the 3- year average of the 99th percentile of the daily maximum 1-hour av erage at each monitor within a n area over each year must not exceed 75 ppb.



### Table 4-1 shows that monitored concentrati ons at both stations are well below the SO 2 

### National Ambient Air Quality Standards (NAAQS). Monitored compliance with the 1-hour SO 2 

### NAAQS is based on the 3-year average of the 99th pe rcentile of the daily maximum 1-hour values.

4.3 AREA CLIMATE AND METEOROLOGY

The southeastern area of the state, where th e McElmo Creek facility is located, can be
characterized as an area of low precipitation, high summer temper atures, and moderate winter temperatures. Meteorological monitoring has no t been conducted onsite at the McElmo Creek facility. UDAQ supplied the pre-processed AE RMET meteorological data for this study, which originates from the Canyonlands Ai rport, northwest of the facility. These data cover the years
2005-2009 and is considered as representative of the southeastern Utah area. Table 4-2 presents a summary wind speed and direction distribution for the five year period. Figure 4-1 presents a graphical depiction of wind speed and direction distribution as a wind rose. The average wind speed was 2.6 meters/second (m/s), or 5.8 mi les per hour (mph). The predominant wind directions were from the west-southwest (11.0% ), from the west (10.3%), and from the northnortheast (10.8%).

An atmospheric stability distribution for this peri od is in Table 4-3. This table shows that neutral (D) and stable (F) conditions are dominant.

### 4-3 **Table 4-2**

**10 METER WIND DATA ANALYSIS FROM 01/01/2005 THROUGH 12/31/2009**  **CANYONLANDS AIRPORT METEOROLOGICAL STATION**

**FREQUENCY OF OCCURRENCE OF WIND SPEED BY DIRECTION**

**+----------WIND SPEED CLASSES (M/S)----------+ AVERAGE**  **0.0- 1.8- 3.3- 5.4 8.4 > WIND DIR 1.8 3.3 5.4 8.4 11.0 11.0 TOTAL SPEED** 

**------------------------------------------------------------------------- N .0248 .0152 .0037 .0014 .0003 .0000 0.045 2.0** 

**NNE .0461 .0224 .0142 .0080 .0020 .0004 0.093 2.5**

**NE .0164 .0071 .0037 .0035 .0010 .0001 0.032 2.6**

**ENE .0199 .0075 .0052 .0042 .0010 .0000 0.038 2.6**

**E .0219 .0123 .0084 .0020 .0001 .0000 0.045 2.2**

**ESE .0238 .0208 .0093 .0005 .0000 .0000 0.054 2.1**

**SE .0267 .0260 .0163 .0030 .0002 .0000 0.072 2.5**

**SSE .0204 .0131 .0083 .0035 .0005 .0000 0.046 2.5**

**S .0153 .0057 .0049 .0046 .0007 .0001 0.031 2.8**

**SSW .0160 .0048 .0063 .0092 .0045 .0007 0.041 4.0**

**SW .0300 .0088 .0126 .0120 .0048 .0007 0.069 3.5**

**WSW .0764 .0148 .0098 .0065 .0019 .0004 0.110 2.0**

**W .0571 .0183 .0173 .0079 .0019 .0006 0.103 2.4**

**WNW .0291 .0158 .0194 .0132 .0039 .0008 0.082 3.5**

**NW .0300 .0281 .0171 .0065 .0028 .0005 0.085 2.9**

**NNW .0210 .0213 .0087 .0016 .0004 .0001 0.053 2.4**

**------------------------------------------------------------------------- TOT: 0.475 0.242 0.165 0.087 0.026 0.004 1.000**  **AVG: 0.9 2.6 4.2 6.7 9.5 13.6 2.6**

**TOTAL NUMBER OF VALID READINGS FOR THIS TABLE => 43456 OUT OF 43456 TOTAL VALID HOURS**  **TOTAL NUMBER OF MISSING HOURS => 368 TOTAL NUMBER OF CALM HOURS => 4806** 

### 4-4 Table 4-3. Annual Stability Class Dist ribution at Canyonlands Airport, Utah.
Stability Class Percent of Occurrence (%)
A 4.2
B 8.5
C 8.4
D 25.0
E 4.1
F 49.7



### Temperature and precipitation c onditions in vicinity of the Mc Elmo Gas Compression Facility are depicted by a long-term climatic monthl y summary (12/8/1904 – 3/31/2005) of data from Blanding, Utah in Table 4-4.

Table 4-4. Monthly Average Temperature an d Total Precipitation at Blanding, Utah.
Month Avg. Temp. Max. ( o F) Avg. Temp. Min. ( o F) Avg. Temp. Mean ( o F) Precipitation Total (inches) January 39.1 17.1 28.1 1.39 February 44.8 22.3 33.6 1.23

March 52.7 27.8 40.3 1.04 April 62.2 34.3 49.3 0.87 May 72.2 42.0 57.1 0.71
June 83.3 50.7 67.0 0.45 July 88.6 57.8 72.2 1.15 August 86.2 56.1 71.1 1.39 September 78.2 48.3 63.3 1.28

October 66.0 37.9 51.9 1.45
November 51.4 26.6 41.0 1.06
December 41.1 19.1 30.1 1.35 Annual Avg. Temp./Annual Total Precip. 63.8 36.7 50.3 13.35WRPLOT View - Lakes Environmental Software

WIND ROSE PLOT Canyonlands Airport Station Meteorological Data

DATE:
4/22/2011 PROJECT NUMBER: 

### 2440-10 Figure 4-1 NORTH

SOUTH WEST EAST 2% 4% 6% 8% 10%

W I N D S P E E D ( m / s )

> = 1 1

. 0

8

. 4

- 1 1

. 0

5

. 4

- 8

. 4

3

. 3

- 5

. 4

1

. 8

- 3

. 3

0

. 4

- 1

. 8
C a l m s : 1 1

. 1 2 %

TOTAL COUNT:

43205 hrs. CALM WINDS:

11.12% DATA PERIOD:

2005-2009 Jan 1 - Dec 31 00:00 - 23:00

AVG. WIND SPEED:

2.64 m/s DISPLAY: Wind Speed Direction (blowing from)

### 5-1 5.0 IMPACT ASSESSMENT APPROACH

This section presents the methodology used to eval uate the potential ambient air quality impacts resulting from the operation of the Main Flare. These analyses are compared against the National Ambient Air Quality Standards (NAAQS) a nd PSD increments presented in Table 5-1.

TABLE 5-1 SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS AND PSD INCREMENTS

NAAQS Class II PSD Averaging Primary Increment Pollutant Time μ g/m 3 (ppm) μ g/m 3 (ppm)
1-hour a 40,000 (35) -- Carbon Monoxide
8-hour a 10,000 (9) -- Annual (arith. Mean) 100 (0.05) 25 (0.013) Nitrogen Dioxide

1-hour b 188 (0.10) --
Ozone 8-Hour c 147(0.08) --

24-hour a 150 (--) 30 (--) Particulates (PM 10 ) Annual (arith. Mean) 50 (--) 17 (--)

24-hour a 35 (--) 9(--) Particulates (PM 2.5 ) Annual (arith. Mean) 15 (--) 4 (--)

Sulfur Dioxide 1-hour 196 (0.075) -- 3-hour a 1,300 (0.50) 512 (0.20)
24-hour a 365 (0.14) 91 (0.035) Annual (arith. Mean) 80 (0.03) 20 (0.008)

Rolling 3-month Average 0.15 (--) -- Lead

Calendar Quarter (arith. mean) 1.5 (--) --

a. Not to be exceeded more than once per year. b. The 3-year average of the 98 th percentile of the daily maximum 1-hour average at each monitor within an area must not exceed 100 ppb. c. The 3-year average of the 4 th highest daily maximum concentrations must not exceed this standard.

### 5-2 5.1 AIR QUALITY MODEL DESCRIPTION

AERMOD (AMS/EPA Regulatory Model), Versi on 09292, was used to assess potential nearfield air quality impacts of the facility. AERM OD has the capability of modeling for both shortterm and long-term averaging periods. The model was run in regulatory default mode with rural dispersion coefficients.

AERMOD is a modeling system consisting of three separate modules: AERMAP, AERMET and
AERMOD.

AERMAP is a terrain preprocessor that uses Digital Elevation Model (DEM) or National Elevation Dataset (NED) electronic files, which are readily availa ble from the Internet, for use with user-generated receptor grids. The output f ile consists of the x, y locations of each receptor, mean sea level (MSL) elevation and hill profile para meter. The hill profile parameter is used in determining plume flow around elevated terrain. Source elevation and receptor elevations and hill heights were determined thr ough AERMAP using NED files.

The meteorological preprocessor AERMET uses hourly surface observations, cloud cover/solar radiation-delta T and upper air parameters from twice-daily vertical samp ling of the atmosphere to create two output files consisting of surface and vertical profile da ta, respectively. Preprocessed AERMET files were obtained from UDAQ for use in this study.

AERMOD directly reads the three output files created by the pre-processing programs, and along
with user-entered source inform ation, predicts ambient air conc entrations for a variety of pollutants and averaging periods ranging from 1-hour to annual.

5.2 MODEL INPUT

The Main Flare is a point (stack) source that rout inely operates in the stand-by mode as reflected in the annual emissions presented as limits in Se ction 3. For modeling purposes, particularly for comparison to short-term standards and PSD increments, the worst-case impacts from the Main Flare would be during an upset episode when all pro cess gas is sent to the flare, rather than reinjected into the ground. Thus, modeled flare st ack parameters were adjusted to reflect the

### 5-3 instantaneous nature of heat release characteristics of a fl are when combusting all process gas rather than re-injecting for input to AERMOD. The algorithm for this characterization is based on the Texas Commission on Environmental Qualit y’s “Technical Basis for Flare Parameters” (September 10, 2004). An effective stack diameter at an assumed stack velocity of 20 m/s at the estimated heat release (in calories per second) of the flare is es timated. An effective stack height
is estimated based on heat release and the physical stack height of th e flare. Table 5-2 presents a summary of these estimates at the four heat co ntent conditions of the flared gas described in
Section 5.4. A radiative loss of zero is assume d for consistency with buoyancy flux estimations from the algorithm used in SCREEN3.

Supplemental modeling was performed to estimate impacts of 1-hour SO 2 

### only, since PM 10 

### emissions are insignificant and previous SCREEN3 modeling of NO x 

### , CO and the other averaging periods for SO 2 

### demonstrated modeled compliance to the applicable standards. VOCs are not modeled directly except as a precursor to ozone. The annual emission limit for VOCs (95.4 tons per year) is below the 100 ton per year criterion typically cited as that level requiring ozone modeling. Previous SCREEN3 modeling assu med flat terrain. AERMOD was run in both
the FLAT and ELEV modes to assess the effects of terrain on modeled 1-hour SO 2 

### impacts and to compare modeled AERMOD impacts to previously modeled SCREEN3 impacts.

5.3 METEOROLOGICAL DATA

The selection of an appropriate meteorological data set for air quality modeling is based on proximity to the project site, similarity of t opography and conformity of the data collection and reporting procedures to PSD m onitoring requirements. Anothe r consideration is that the meteorological data can be readil y processed into a format compa tible for use in air dispersion modeling.

For this study, modeling was conducted using a Divi sion-furnished five ye ar (2005-2009) of preprocessed 10-meter tower data from the Canyon lands Airport (KCNY) st ation near Moab, UT for surface data, and concurrent upper air data fr om Grand Junction, CO. The base elevation of the KCNY meteorological monitoring site is 1387.8 meters, which was used as input for
AERMOD.

### 5-4 Table 5-2. Estimated Flare Stack Parameters for AERMOD Input

Assumptions: Actual Stack Height (m.), H s : 59.45 Stack Temperature ( o K), T s : 1273 Stack Velocity (m/s), V s : 20.0 Flare Gas Flow Rate (scf/hr): 618104.0 Ambient Temperature ( o K), T: 294.3 (Assumed as 70.0 o F.)

1. H sl , Effective Stack Height (m.) = H s + (4.56 x 10 -3 ) * (H r /4.1868) 0.478 where,
H r = Net Heat Release (Joules/sec) = (1 - F) H F = Radiative Loss Factor, 0 (2008 SCREEN3 modeling): 0.0 % H = Heat release at from flared gas at a particular heat content, in joules/sec 1 BTU = 1055.0 Joules = 252 Calories

Heat Content Heat Release, H Net Heat Release, H r Effective Stack Height, H sl (BTU/SCF) (BTU/sec) (Joules/sec) (Joules/sec) (m.) 300 51508.7 54341643.3 54341643.33 70.91 443 76061.1 80244493.3 80244493.32 73.25 538.8 92509.6 97597591.4 97597591.43 74.61 682.4 117165.0 123609124.7 123609124.7 76.42

2. d s , Effective Stack Diameter (m.) = 0.03249 * ((H r /V s ) * (T s /(T * (T s - T)))) 0.5
where H r , V s , T s and T are input variables with assigned values described above

Heat Content Net Heat Release, H r Stack Velocity, V s Stack Temp., Ts Ambient Air Temp., T Effective Stack Diameter, d s (BTU/SCF) (Joules/sec) (m/sec) ( o K) ( o K) (m.) 300 54341643.33 20.0 1273.0 294.3 3.561 443 80244493.3 20.0 1273.0 294.3 4.327 538.8 97597591.4 20.0 1273.0 294.3 4.772 682.4 123609124.7 20.0 1273.0 294.3 5.370

3. Flare Stack Parameters Used for Each Flare Gas Heat Content Scenario in AERMOD

Heat Content Effective Stack Height, H sl Effective Stack Diameter, d s Stack Temp., Ts Stack Velocity, V s SO 2 Emission

Rate (BTU/SCF) (m.) (m.) ( o K) (m/sec) (g/s) 300 70.908 3.561 1273.0 20.00 9.21 443 73.254 4.327 1273.0 20.00 9.21 538.8 74.609 4.772 1273.0 20.00 9.21 682.4 76.421 5.370 1273.0 20.00 9.21

### 5-5 5.4 SOURCE CHARACTERISTI CS AND EMISSION RATES

5.4.1 Flare Rate and Heat Release

Short-term pollutant emission rates were estim ated by assuming that the maximum volume of process gas that could be generated from the well fi eld would be sent to the flare at four different heat content values (in BTU/scf). These four h eat content values represent a range of estimates including the lowest allowable LHV, the lowe st LHV from 2004 gas analyses, the lowest LHV from 2005-08 gas analyses and the highest LHV from 2005-08 gas analyses data. The lowest value input was 300 BTU/scf, which is the lo west allowable LHV as stated in 40 CFR 60.18(c)(3)(ii). The next lowest value utilized was 443 BTU/scf, which is the lowest of four 2004 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 were 443, 505, 512, and 453 BTU/scf, respectively.)
The LHV of 443 BTU/scf was utilized due to th e assumption that it would provide the least amount of heat rise, thus produci ng the lowest effective release he ight. The lowest and highest LHVs from 2005-08 gas analyses data of 538.8 a nd 682.4 BTU/scf, respectively, were also used for emission estimation. The resultant range of BTU contents and effective release heights were
modeled to evaluate the sensitiv ity of impacts to each emission ra te/effective release height and
diameter combination.

The maximum flare rate utilized was 689,423 acf/h r (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 ne w 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 ex it velocity as specified by 40 CFR 60.18, which is 66.98 ft/s.

The heat released from the flare tip was then cal culated 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 cal V LHV s cal heat 3600 ) 1644

. 252 )( )( ( ) / ( =

### 5-6 Where: LHV = lower heating va lue of gas burned (BTU/scf) V = 618,104 scf/hr.

5.4.2 Flare Height



### The actual flare stack height of 195 feet wa s taken from drawing D-SA-107 as provided by Zeeco, Inc. from 1991. This measurement was fi eld verified to ensure proper stack height.

5.4.3 Modeled Emission Rates



### The emission factors for NO x 

### and CO were derived by the Chemical Section of the Texas Commission on Environmental Quality NSR Di vision based on data published in the 1983
Chemical Manufacturer's Association document entitled "A Report On A Flare Efficiency Study." The factors used were as follows:

NO x 

### = 0.0641 lb/MMBTU
CO = 0.5496 lb/MMBTU.

Therefore, the equation used to calculate the emission rate for NO x 

### and CO contaminants at the specified LHV is as follows:

s hr lb g MMBTU lb EF BTU MMBTU scf BTU LHV hr scf V s g rate 3600 * 59

. 453 * * 10 * * ) / ( 6 

### =



### Where: V = 618,104 scf/hr LHV = lower heating value of gas burned (BTU/scf) EF = emission factor (lb/MMBTU).

Tests subsequent to the March 22, 2007 applicati on submittal at the McElmo site indicated the plant inlet gas contains approximately 500 ppm H 2 

### S. However, it was assumed that the flared gas contains 700 ppm H 2 

### S to estimate SO 2 

### emissions input to AERMOD. This H 2 

### S value was

### 5-7 used in order to provide a conservative estimate of SO 2 

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

rate (g/s) = (618,104 scf/hr * 700 ppm * 64 lb/lb-mole SO 2 )/(380 scf/lb-mole * 1,000,0 00 ppm)= 72.87 lbSO 2 /hr



### In summary, the stack parameters and estimated emission rates for the Main Flare at the four representative heat content values during upset conditions are summarized below in Table 5-3.

Table 5-3
Modeled Stack Parameters and Emissions for the Main Flare (Maximum Volumetric Process Gas Flow of 618,104 SCF/hr)

Heat
Content (BTU/SCF) Stack Height

(m.) Effective
Release Height (m.) Effective
Stack Dia. (m.) Stack Velocity

(m/s) Short-Term
NO x Emission Rate (gm/sec) Short-Term
SO 2 Emission Rate (gm/sec) Short-Term
CO Emission Rate (gm/sec)
300 59.45 70.908 3.561 20.0 1.50 9.18 12.84
443 59.45 73.254 4.327 20.0 2.21 9.18 18.96
538.8 59.45 74.609 4.772 20.0 2.69 9.18 23.06
682.4 59.45 76.421 5.370 20.0 3.41 9.18 29.21



### 5.5 RECEPTOR SELECTION



### Discrete receptors in UTM Zone 12 NAD83 coor dinates were processed by AERMAP using 10-
meter NED data with the following grid resolutions:

• 

### A single ring of receptors 200 meters from the center point of the flare

• 

### 100 meter spaced grid out to 2,200 meters from the flare

• 

### 250 meter spaced grid from 2.2 to 10 kilometers from the flare

• 

### 500 meter spaced grid from 10 to 20 kilometers from the flare

Additional blocks of 100-meter spaced grids were also used to determine maximum concentrations within the coarse grids. Figure 5-1 presents a plot of the modeled receptor grid used for this study.

### 5-8 5.6 BACKGROUND MODELED SOURCES



### Data on background SO 2 

### emission sources in the region surrounding the McElmo Creek Gas Plant were acquired for modeling of cumulativ e impacts because maximum 1-hour SO2 impacts from the flare exceed the 1- hour SIL of 7.9 μg/m 3 

### . The following agencies were contacted to acquire background SO 2 

### emissions data:

1. Utah Department of Air Quality (UDAQ) 2. Colorado Air Pollution Control Division (CAPCD) 3. Southern Ute Indian Tribe Air Quality Program
4. Ute Mountain Indian Tribe

The following responses were received from these agencies:

1. The UDAQ provided background SO 2 

### data from a facility located south of Blanding with a total of 0.7 tons per year (tpy) average fo r the last two years and is the only facility reporting emissions within 50 km. of the Mc Elmo Creek Gas Plant, approximately 40 km. away.

2. The CAPCD provided background SO 2 

### data from various facilities with total emissions of approximately 34 tpy, located approxima tely 15 to 50 km. from the McElmo Creek
Gas Plant.

3. Responses received from the Tribal agenci es indicated that information on background
SO 2 

### emission source data from facilities on Tribal Land are not publicly available

An Internet search for recent NEPA studies pe rformed in the Four Corners Area found that the only available study was the Desert Rock Energy Project Draft EIS. SO 2 

### emission source data in this document are from large power plant sour ces only, located at least 100 km. from the McElmo Creek Gas Plant. Therefore, it is not appropriate to include these data to model
cumulative 1-hour SO 2 

### impacts from the flar e and background sources.

.

### 5-9 The flare was modeled with all background SO 2 

### data provided by the UDAQ and the CAPCD and added to the maximum daily monitored 1-hour SO 2 

### concentration of 79 μg/m 3 

### for comparison to the 1-hour SO 2 

### standard of 196 μg/m 3 

### . The EPA guidance memo, dated March 1, 2011, on modeling of 1-hour NO 2 

### and SO 2 

### suggests “that the emphasis on determining which nearby sources to include in th e modeling analysis should focu s on the area within about 10 kilometers of the project location”. The basis of this statement is that modeled 1-hour NO 2 

### and
SO 2 

### impacts decrease significantly more with distance than wh en the longer-term averaging periods are modeled. However, all bac kground sources from the UDAQ and CAPCD were included in the modeling even though the closes t emission source is located at least 15
kilometers from the McElmo Creek Gas Plant.

Modeled background source input for 1-hour SO 2 

### is presented in Table 5-4.Table 5-4. Modeled Background Source InputPoint Source Emission Rates and Stack ParametersLocation SO2Easting Northing Elevation 1-HourStackHeight TemperatureExitVelocityExitDiameterFacility Name (m) (m) (m) (g/s) (m) (oK) (m/s) (m)McElmo CreekMcElmo Creek Plant 659259.7 4125275.6 1459.59.210070.91 1273.00 20.000 3.56Utah SourcesDenison Mines Corp.: White Mesa Mill 634400.0 4159100.0 1752.61.1075E-0526.82 293.15 0.170 0.10Denison Mines Corp.: White Mesa Mill 634400.0 4159100.0 1752.63.2219E-0610.67 394.26 0.200 0.70Denison Mines Corp.: White Mesa Mill 634400.0 4159100.0 1752.61.2255E-053.05 295.37 0.080 0.30Denison Mines Corp.: White Mesa Mill 634400.0 4159100.0 1752.63.6879E-0526.82 293.15 0.170 0.10Denison Mines Corp.: White Mesa Mill 634400.0 4159100.0 1752.61.5672E-0426.82 308.15 0.400 0.24Colorado SourcesQuestar E&P -Spargo #1-36 675928.3 4162567.7 1996.66.6107E-052.13 644.26 9.780 0.10Questar E&P - Island ButteA 677249.2 4159645.1 1986.02.8767E-053.66 838.71 3.810 0.25Questar E&P - Island ButteA 677249.2 4159645.1 1986.02.8767E-053.66 838.71 1.280 0.15Questar E&P - Island Butte#3 677724.6 4158971.0 1981.91.2658E-043.05 583.15 0.000 0.20DJ Simmons - Compressor #1 677622.4 4163863.7 2027.01.6078E-040.00 255.37 0.000 0.10Questar Exploration - Spargo No 2 675923.5 4161781.3 1988.78.4547E-053.35 830.37 41.240 0.13Kinder Morgan CO2 Co. -Yellow Jacket H10 695330.9 4149292.4 2024.92.4452E-016.10 644.26 2.530 1.05Kinder Morgan CO2 Co. -Yellow Jacket H10 695330.9 4149292.4 2024.92.4452E-016.10 644.26 2.530 1.05Kinder Morgan CO2 Co. -Hovenweep Central 687300.6 4151258.9 1965.22.4228E-016.10 644.26 2.530 1.05Kinder Morgan CO2 Co. -Hovenweep Central 687300.6 4151258.9 1965.22.4228E-016.10 644.26 2.530 1.05Questar E&P Cutthroat Battery A 683113.0 4149203.7 1871.61.4309E-043.35 752.04 26.760 0.15Questar E&P Cutthroat Battery A 683113.0 4149203.7 1871.68.2878E-052.44 872.59 53.890 0.09Questar E&P Cutthroat Battery A 683113.0 4149203.7 1871.64.0907E-055.79 807.59 4.660 0.30Questar E&P Cutthroat Battery B 684827.8 4145395.2 1904.09.8786E-053.35 752.04 26.760 0.15Questar E&P Cutthroat Battery B 684827.8 4145395.2 1904.06.9041E-050.61 501.48 5.390 2.44Questar E&P Cutthroat Battery B 684827.8 4145395.2 1904.02.1374E-053.66 866.48 3.810 0.10Questar Exploration - Mcclean Basin #2 683232.7 4148526.9 1846.24.7466E-052.44 841.48 29.690 0.10Questar E & P- Island Butte - B 681223.5 4156947.6 1982.57.7671E-055.18 522.04 4.720 0.44Smith Energy Lp 1988 Cache Oil Field 674969.6 4124174.4 1531.11.3808E-043.05 255.37 23.990 1.52Questar Exploration - Cutthroat #5 684827.4 4145394.4 1904.05.1666E-052.13 877.59 38.130 0.76Questar Exploration - Island Butte #7AH 680030.7 4157102.6 1978.41.6570E-053.05 699.82 2.870 0.15Questar Exploration - Island Butte #7AH 680030.7 4157102.6 1978.42.2151E-053.05 699.82 4.180 0.15Questar Expl And Prod - Cutthroat #9 682805.0 4151855.0 1838.83.0205E-054.57 569.26 8.530 0.10Questar Exploration - Cutthroat #14 684630.6 4143114.5 1898.32.4567E-054.57 568.15 0.150 1.26Questar Exploration - Cutthroat #8 684833.6 4144650.5 1898.91.9792E-052.13 588.71 0.000 0.08Table 5-4 (Continued). Modeled Background Source InputArea Source Emission Rates and Source ParametersLocation LengthEasting Northing ElevationSO2Emission RateReleaseHeightX Y(m) (m) (m) (g/s) (g/s-m2) (m) (m) (m)Utah SourcesDenison Mines Corp.: White Mesa Mill 634350.0 4159050.0 1752.6 0.01971.9734E-063.05 100 100640000 645000 650000 655000 660000 665000 670000 675000 UTM Easting (m) NAD83, Zone 12 4110000 4115000 4120000 4125000 4130000 4135000 4140000 4145000UTM Northing (m)NAD83, Zone 12

Figure 5-1 McElmo Creek Gas Plant 1-Hour SO2 Modeling Modeled Receptor Grid Including Fine Grids

### 6-1 6.0 AIR QUALITY IMPACTS



### This section presents modeled air quality impact s of the Main Flare facility to demonstrate compliance with the 1-hour SO 2 

### National Ambient Air Quality Standards (NAAQS), using AERMOD. A Prevention of Significant Deterior ation Increment for Cl ass II Areas for 1-hour
SO 2 

### has not been established. Air quality impact s are presented from the Main Flare alone and combined with modeled background sources w ith a representative ambient air background concentration to assess cumulative impacts.

As discussed in the previous sec tion, several assumptions were ma de to conservatively calculate emission rates from the Main Flare for use in this modeling analysis. These assumptions
included:

1. Consideration of a range of heat value ratings and corres ponding effective release heights for the gas at McElmo to evaluate a nd identify maximum im pacts produced by the McElmo Main Flare; 2. The maximum design flare rate of 14.83 MCFD; and
3. An H 2 

### S concentration of 700 ppm instead of previously measured values of approximately 450 to 500 ppm.

Emission limitations established by the Consent Decree for the Ma in Flare are 60 tons per year
of SO 2 

### , 73 tons per year of CO, 13.4 tons per year of NO x 

### , and 94.5 tons per year of VOC. However, the worst-case conditions based on th e modeled maximum flare rate of 14.83 MCFD
and LHV of 682.4 BTU/scf result in em issions of 319.12 tons per year of SO 2 

### , 1,015.41 tons per year of CO, and 118.54 tons per year of NO x 

### . These very conservative worst-case conditions result in emission rates in the analysis that are at least five times greater than current air permit limits. In addition, the actual fi eld conditions are not capable of sustaining a flow rate of 14.83
MCFD. The remainder of this section will show that even with these worst-case emission estimates that far exceed the current air perm it limits and actual flow rate conditions, the modeling results show no exceedances of the 1-hour SO 2 

### NAAQS.

A DVD of AERMOD model run i nput and output files, meteorol ogical data and AERMAP files is contained in Appendix A. Model runs include estimated SO 2 

### impacts for process gas with a heat content of 300, 443, 538.8 and 682.4 BTU/SCF.

### 6-2 6.1 SULFUR DIOXIDE (SO 2 

### )



### The Main Flare was modeled at the heat content scenarios of 300, 443, 538.8 and 682.4 BTU/SCF. The maximum modeled impact concen trations from AERMOD occurred with a flare
heat content of 300 BTU/SCF. Ho wever, the results shown in Tables 6-1 and 6-2 for the FLAT and ELEV runs, respectively reflec t all modeled heat content sc enarios as well as discrete regional sources. Additionally, the maximum 1-hour background SO 2 

### concentration was
obtained and added to the maximum modeled SO 2 

### impacts from the Main Flare and regional
sources to obtain an estimate of cumu lative impacts for comparison to the SO 2 

### NAAQS.

Table 6-1. Comparison of Modeled Cumulative SO 2 

### Impacts to the 1-Hour NAAQS - FLAT

Flare Heat Content Maximum Modeled

Year Maximum Modeled Concentration Monitored Background Concentration Maximum Cumulative Concentration National Ambient Air Quality Std. Percent of NAAQS (ug/m 3 ) (ug/m 3 ) (ug/m 3 ) (ug/m 3 ) (%)

300 2009 8.57 79 87.57 196.5 44.6 443 2009 5.91 79 84.91 196.5 43.2 538.8 2009 4.81 79 83.81 196.5 42.7 682.4 2009 4.24 79 83.24 196.5 42.4



### Table 6-2. Comparison of Modeled Cumulative SO 2 

### Impacts to the 1-Hour NAAQS - ELEV

Flare Heat Content Maximum Modeled

Year Maximum Modeled Concentration Monitored Background Concentration Maximum Cumulative Concentration National Ambient Air Quality Std. Percent of NAAQS (ug/m 3 ) (ug/m 3 ) (ug/m 3 ) (ug/m 3 ) (%)

300 2005 26.76 79 105.76 196.5 53.8 443 2005 19.01 79 98.01 196.5 49.9 538.8 2005 16.35 79 95.35 196.5 48.5 682.4 2005 13.46 79 92.46 196.5 47.0

### 6-3 Figure 6-1 presents a con centration contour plot of maximum modeled 1-hour SO 2 

### impacts from the 300 BTU/SCF heat content input scenario w ith AERMOD in the ELEV mode. To illustrate modeled impacts as a function of flare gas heat content input, Figure 6-2 presents a concentration contour plot of maximum modeled 1-hour SO 2 

### impacts from the 682.4 BTU/SCF heat content input scenario with AERMOD in the ELEV mode.

The predicted maximum 1-hour averaged concen tration from the Main Flare and regional sources is 26.76 μg/m 3 

### , respectively, located approximately 15.5 kilometers from the flare stack.
This maximum concentration added to the background concentration of 79 μg/m 3 

### results in a cumulative concentration of 105.76 μg/m 3 

### , 53.8% of the 1-hour averaged NAAQS of 196 μg/m 3



### .640000 645000 650000 655000 660000 665000 670000 675000 UTM Easting (m) Zone 12, NAD83 4110000 4115000 4120000 4125000 4130000 4135000 4140000 4145000UTM Northing (m)Zone 12, NAD83

Figure 6-1 McElmo Creek Gas Plant Maximum 1-Hour SO2 Modeling Results Flare at 300 btu/scf Including Background Sources Model Year 2005640000 645000 650000 655000 660000 665000 670000 675000 UTM Easting (m) Zone 12, NAD83 4110000 4115000 4120000 4125000 4130000 4135000 4140000 4145000UTM Northing (m)Zone 12, NAD83

Figure 6-2 McElmo Creek Gas Plant Maximum 1-Hour SO2 Modeling Results Flare at 682.4 btu/scf Including Background Sources Model Year 2005

### 7-1 7.0 REFERENCES



### Chemical Manufactturer’s Asso ciation, 1983. “A Report on a Flare Efficiency Study”, referenced by the Texas Commission on Envi ronmental Quality NSR Division, Chemical
Section

Consent Decree, United States of America v. Mobil Exploration & Producing, U.S., Inc., DOJ Case No. 90-5-2-1-2237, filed June 8, 2005 in Un ited States District Court, District of
Utah.

Texas Commission on Environmental Quality, 2004. “Technical Basis for Flare Parameters”, September 10, 2004, Austin, TX.

### APPENDIX A DVD WITH AERMOD MODEL INPUT & OUTPUT FILES,
METEOROLOGICAL DATA AND AERMAP FILES