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: 1 - hr SO 2 Modeling Results of McElmo Creek Gas Plant Modeling Results of McElmo Creek Gas Plant Modeling Results of McElmo Creek Gas Plant Flare Stack Scott Bohning Scott Bohning to: thormel 01/31/2011 07:34 AM Cc: pflynn, Andrew Chew Archive: This message is being viewed in an archive .

Tom -

Utah's inventory may well be enough, but I do not what geographic coverage it has, also major vs. minor sources... default is to look 50 km out from signifiant impact area around the source (more distant minor sources could be omitted). That would have overlap with Navajo Nation land, for which Utah may not have a lot of information. Either way, it would be good to have some "due diligence" assessment of what's it in the area, i.e. some corroboration from other sources of information, as a check.

- Scott B.

"Tom Hormel" 01/28/2011 08:28:50 AM Scott,

From: "Tom Hormel" <thormel@mcvehil-monnett.com> To: Scott Bohning/R9/USEPA/US@EPA Cc: <pflynn@rnrc.net> Date: 01/28/2011 08:28 AM Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

Per my telephone message, I can proceed with the cu mulative modeling. However, I want to confirm that contacting the Utah Division of Air Quality to obta in an background SO2 emission inventory is sufficie nt for this modeling. If you have a preferential approach for compiling the background SO2 emission inventor y that differs from my proposed approach, please let me know.

Thanks,

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

From: Bohning.Scott@epamail.epa.gov [mailto:Bohning.Scott@epamail.epa.gov] Sent: Thursday , January 27, 2011 5:23 PM To: thormel@mcvehil-monnett.com Cc: Chew.Andrew@epamail.epa.gov Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Tom -

Again I apologize for the delay... I did finally get a chance to look some more at what you want on flaremodeled parameters and the AERMOD output

. Since the results are above the interim SO 2 SIL of ( about )

7.8 μg/m3, it indeed appears that cumulative modeling will be needed, including nearby sources. If you wish to discuss, I am free for a call most times during next week (but late mornings tend to be booked, also mid-afternoon Wed. and Thurs.).

- Scott B.

-- =+=+=+=+=+=+=+=+=+=+=+=+=+=+= "Scott Bohning" <bohning.scott@epa.gov> U.S. EPA Region 9, AIR-7 415/947-4127 fax-3579

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

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

Date: 01/21/2011 08:47 AM
Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

I am resending the attachments from my last two e-m ails so that they are not zipped.

Sorry about the inconvenience.

Thanks,

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

- monnett

. com -----Original Message----- From: Bohning.Scott@epamail.epa.gov [ mailto : Bohning

. Scott @ epamail

. epa

. gov ] Sent: Thursday , January 20, 2011 5:26 PM To: thormel@mcvehil-monnett.com Subject: Re: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Tom -

Sorry that I have not had time to do this justice, & I am out Fri. 1/2... I will have to think some more to confirm, but right now it seems to me that you could use AERMOD flat terrain only if terrain really is pretty flat. I'm assuming it is not, so you would be stuck with the higher, complex terrain values, adn the need for a background inventory.- Scott B.

-- =+=+=+=+=+=+=+=+=+=+=+=+=+=+= "Scott Bohning" <bohning.scott@epa.gov> U.S. EPA Region 9, AIR-7 415/947-4127 fax-3579

P.S. On the attachment, I do have "Flare Stack Parameter Estimation.pdf" from 12/22, however, per note at end of this e-mail, perhaps you could resend your later attachment, but with Zip file(s) renamed to have different extension, like ".zi". ( our e-mail system strips all incoming and outgoing ".zip" files on the dubious grounds that they may contain a virus!)

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

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

Cc: <pflynn@rnrc.net>

Date: 01/17/2011 09:59 AM
Subject: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

Per my telephone message to you this morning, below is a copy of our 12/22/10 e-mail to you discussing initial AERMOD modeling results for 1-hour SO2 impa cts from McElmo Creek Gas Plant's flare stack. Please review so we can discuss these results and p roceed with any additional modeling that may be required. The two files referenced in the 12/22 e- mail are attached for your convenience.

We look forward to your response.

Thanks,

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

E-mail from December 22, 2010, 3:29 PM MST

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 charact erized as a point source by estimating effective st ack diameter and stack height with stack velocity and t emperature set at values consistent with SCREEN3 guidance. The flare stack was modeled at four flar e gas heat content values (i.e., 300, 443. 538.8 an d 682.4 BTU

/ SCF ) with a constant SO2 emission rate based on 700 ppmv H 2S. 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 modeli ng report submitted in 2008 is also attached to show the consistency between the model input for AE RMOD and the previous SCREEN3 modeling.

We ran the AERMOD both in the flat and complex terr ain modes and get mixed results when comparing the maximum modeled 1-hour SO2 impacts to the 1 hou r SO2 SIL of 7.9 ug / m^3. These modeling results are:

1. In the flat terrain mode, maximum 1--hour SO2 i mpacts 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 woul d be consistent with the simple terrain assumed for the 2008 SCREEN3 modeling, we demonstrate modeled 1-hou r SO2 impacts below the SIL by citing the results for the three higher heat content cases. R ecent monthly flare gas analysis data suggest that the lowest heat content of the flare gas is approximate ly 500 BTU / SCF and that the 300 BTU / SCF is an unrealistically conservative case. However, if we rely on the complex terrain results, regional model ing with background SO2 emission sources may be necessa ry because of the results described above.

We would like to discuss these modeled impacts to d etermine 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

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### [attachment "Flare Stack Parameter Estimation

_ 122010.xls" deleted by Scott Bohning/R9/USEPA/US] [attachment "SCREEN3 SO2 Runs

_ 2008.pdf" deleted by Scott Bohning/R9/USEPA/US] [attachment "AERMOD Results

_ 1 hr SO2.pdf" deleted by Scott Bohning/R9/USEPA/US]